diff --git a/akka-cluster/src/main/scala/akka/cluster/ClusterDaemon.scala b/akka-cluster/src/main/scala/akka/cluster/ClusterDaemon.scala
index 3bad4eb512..5b9cbab9d3 100644
--- a/akka-cluster/src/main/scala/akka/cluster/ClusterDaemon.scala
+++ b/akka-cluster/src/main/scala/akka/cluster/ClusterDaemon.scala
@@ -555,7 +555,7 @@ private[cluster] final class ClusterCoreDaemon(publisher: ActorRef) extends Acto
       // leader handles merge conflicts, or when they have different views of how is leader
       val handleMerge = localGossip.leader == Some(selfAddress) || localGossip.leader != remoteGossip.leader
       val comparison = remoteGossip.version tryCompareTo localGossip.version
-      val conflict = !comparison.isDefined
+      val conflict = comparison.isEmpty
 
       if (conflict && !handleMerge) {
         // delegate merge resolution to leader to reduce number of simultaneous resolves,
@@ -574,25 +574,23 @@ private[cluster] final class ClusterCoreDaemon(publisher: ActorRef) extends Acto
 
       } else {
 
-        val (winningGossip, talkback) = comparison match {
+        val (winningGossip, talkback, newStats) = comparison match {
           case None ⇒
             // conflicting versions, merge, and new version
-            ((remoteGossip merge localGossip) :+ vclockNode, true)
+            ((remoteGossip merge localGossip) :+ vclockNode, true, stats)
           case Some(0) ⇒
             // same version
-            stats = stats.incrementSameCount
             // TODO optimize talkback based on how the merged seen differs
-            (remoteGossip mergeSeen localGossip, !remoteGossip.hasSeen(selfAddress))
-          case Some(x) if (x < 0) ⇒
+            (remoteGossip mergeSeen localGossip, !remoteGossip.hasSeen(selfAddress), stats.incrementSameCount)
+          case Some(x) if x < 0 ⇒
             // local is newer
-            stats = stats.incrementNewerCount
-            (localGossip, true)
+            (localGossip, true, stats.incrementNewerCount)
           case _ ⇒
             // remote is newer
-            stats = stats.incrementOlderCount
-            (remoteGossip, !remoteGossip.hasSeen(selfAddress))
+            (remoteGossip, !remoteGossip.hasSeen(selfAddress), stats.incrementOlderCount)
         }
 
+        stats = newStats
         latestGossip = winningGossip seen selfAddress
 
         // for all new joining nodes we remove them from the failure detector
@@ -1080,7 +1078,7 @@ private[cluster] case class ClusterStats(
   def incrementOlderCount(): ClusterStats =
     copy(olderCount = olderCount + 1)
 
-  def +(that: ClusterStats): ClusterStats = {
+  def :+(that: ClusterStats): ClusterStats = {
     ClusterStats(
       this.receivedGossipCount + that.receivedGossipCount,
       this.mergeConflictCount + that.mergeConflictCount,
@@ -1091,7 +1089,7 @@ private[cluster] case class ClusterStats(
       this.olderCount + that.olderCount)
   }
 
-  def -(that: ClusterStats): ClusterStats = {
+  def :-(that: ClusterStats): ClusterStats = {
     ClusterStats(
       this.receivedGossipCount - that.receivedGossipCount,
       this.mergeConflictCount - that.mergeConflictCount,
diff --git a/akka-cluster/src/main/scala/akka/cluster/Gossip.scala b/akka-cluster/src/main/scala/akka/cluster/Gossip.scala
index 7fdfe1b198..ea7328f84f 100644
--- a/akka-cluster/src/main/scala/akka/cluster/Gossip.scala
+++ b/akka-cluster/src/main/scala/akka/cluster/Gossip.scala
@@ -117,7 +117,7 @@ private[cluster] case class Gossip(
    * Has this Gossip been seen by this address.
    */
   def hasSeen(address: Address): Boolean = {
-    overview.seen.get(address).fold { false } { _ == version }
+    overview.seen.get(address).exists(_ == version)
   }
 
   /**
diff --git a/akka-cluster/src/multi-jvm/scala/akka/cluster/StressSpec.scala b/akka-cluster/src/multi-jvm/scala/akka/cluster/StressSpec.scala
index 03e4609faa..b77e623682 100644
--- a/akka-cluster/src/multi-jvm/scala/akka/cluster/StressSpec.scala
+++ b/akka-cluster/src/multi-jvm/scala/akka/cluster/StressSpec.scala
@@ -213,7 +213,7 @@ object StressMultiJvmSpec extends MultiNodeConfig {
     var nodeMetrics = Set.empty[NodeMetrics]
     var phiValuesObservedByNode = {
       import akka.cluster.Member.addressOrdering
-      immutable.SortedMap.empty[Address, Set[PhiValue]]
+      immutable.SortedMap.empty[Address, immutable.SortedSet[PhiValue]]
     }
     var clusterStatsObservedByNode = {
       import akka.cluster.Member.addressOrdering
@@ -235,7 +235,7 @@ object StressMultiJvmSpec extends MultiNodeConfig {
     def receive = {
       case ClusterMetricsChanged(clusterMetrics) ⇒ nodeMetrics = clusterMetrics
       case PhiResult(from, phiValues)            ⇒ phiValuesObservedByNode += from -> phiValues
-      case StatsResult(from, stats) => clusterStatsObservedByNode += from -> stats
+      case StatsResult(from, stats)              ⇒ clusterStatsObservedByNode += from -> stats
       case ReportTick ⇒
         log.info(s"[${title}] in progress\n${formatMetrics}\n\n${formatPhi}\n\n${formatStats}")
       case r: ClusterResult ⇒
@@ -252,7 +252,7 @@ object StressMultiJvmSpec extends MultiNodeConfig {
 
     def maxDuration = results.map(_.duration).max
 
-    def totalClusterStats = results.map(_.clusterStats).foldLeft(ClusterStats()){_ + _}
+    def totalClusterStats = results.foldLeft(ClusterStats()){_ :+ _.clusterStats}
 
     def formatMetrics: String = {
       import akka.cluster.Member.addressOrdering
@@ -286,11 +286,11 @@ object StressMultiJvmSpec extends MultiNodeConfig {
         import akka.cluster.Member.addressOrdering
         val lines =
           for {
-            (monitor, phiValues) ← phiValuesObservedByNode.toSeq
-            phi ← phiValues.toSeq.sortBy(_.address)
+            (monitor, phiValues) ← phiValuesObservedByNode
+            phi ← phiValues
           } yield formatPhiLine(monitor, phi.address, phi)
 
-        (formatPhiHeader +: lines).mkString("\n")
+        lines.mkString(formatPhiHeader + "\n", "\n", "")
       }
     }
 
@@ -299,16 +299,9 @@ object StressMultiJvmSpec extends MultiNodeConfig {
     def formatPhiLine(monitor: Address, subject: Address, phi: PhiValue): String =
       s"${monitor}\t${subject}\t${phi.count}\t${phi.countAboveOne}\t${phi.max.form}"
 
-    def formatStats: String = {
-      if (clusterStatsObservedByNode.isEmpty) ""
-      else {
-        val lines =
-          for {
-          (monitor, stats) ← clusterStatsObservedByNode.toSeq
-        } yield s"${monitor}\t${stats}"
-        ("ClusterStats" +: lines).mkString("\n")
-      }
-    }
+    def formatStats: String =
+      (clusterStatsObservedByNode map { case (monitor, stats) => s"${monitor}\t${stats}" }).
+        mkString("ClusterStats\n", "\n", "")
   }
 
   /**
@@ -377,7 +370,8 @@ object StressMultiJvmSpec extends MultiNodeConfig {
               math.max(previous.max, φ))
           }
         }
-        reportTo foreach { _ ! PhiResult(cluster.selfAddress, phiByNode.values.toSet) }
+        val phiSet = immutable.SortedSet.empty[PhiValue] ++ phiByNode.values
+        reportTo foreach { _ ! PhiResult(cluster.selfAddress, phiSet) }
       case state: CurrentClusterState ⇒ nodes = state.members.map(_.address)
       case memberEvent: MemberEvent   ⇒ nodes += memberEvent.member.address
       case ReportTo(ref)              ⇒ reportTo = ref
@@ -406,7 +400,7 @@ object StressMultiJvmSpec extends MultiNodeConfig {
 
     def receive = {
       case StatsTick ⇒
-        val res = StatsResult(cluster.selfAddress, cluster.readView.latestStats - startStats)
+        val res = StatsResult(cluster.selfAddress, cluster.readView.latestStats :- startStats)
         reportTo foreach { _ !  res }
       case ReportTo(ref) ⇒
         reportTo = ref
@@ -599,8 +593,11 @@ object StressMultiJvmSpec extends MultiNodeConfig {
   case object RetryTick
   case object ReportTick
   case object PhiTick
-  case class PhiResult(from: Address, phiValues: Set[PhiValue])
-  case class PhiValue(address: Address, countAboveOne: Int, count: Int, max: Double)
+  case class PhiResult(from: Address, phiValues: immutable.SortedSet[PhiValue])
+  case class PhiValue(address: Address, countAboveOne: Int, count: Int, max: Double) extends Ordered[PhiValue] {
+    import akka.cluster.Member.addressOrdering
+    def compare(that: PhiValue) = addressOrdering.compare(this.address, that.address)
+  }
   case class ReportTo(ref: Option[ActorRef])
   case object StatsTick
   case class StatsResult(from: Address, stats: ClusterStats)
@@ -831,7 +828,7 @@ abstract class StressSpec
     val returnValue = thunk
 
     clusterResultAggregator !
-      ClusterResult(cluster.selfAddress, (System.nanoTime - startTime).nanos, cluster.readView.latestStats - startStats)
+      ClusterResult(cluster.selfAddress, (System.nanoTime - startTime).nanos, cluster.readView.latestStats :- startStats)
 
     returnValue
   }