Akka.NET suffers from problems with the Helios transport right now, I don't think the Helios transport do more than a few thousand messages per sec ATM. That being said, there is a new transport coming in Akka.NET 1.5 where we do 100 000 messages per sec in our experiments, so that is a huge improvement.

But that is still more than 8 times slower than GAM.

The reason for Akka.NET (and JVM Akka) having trouble in this area is that every message comes with a sender ActorRef that needs to be resolved. even if the target doesn't touch that ActorRef. The serialization mechanism there is also a lot more complicated.