Moving to Akka 2.0.5. Unfortunately, that doesn’t solve our scheduling problem (=> at least 100ms gap between schedule() calls). Apparently, it was fixed in 2.1.0, but that requires updating to scala 2.10 and updating other dependent libraries.
Replaced all context.system.scheduler.schedule with scheduleAtFixedRate to avoid the 100ms problem. We might come back to Akka once we update to newer versions that have fixed the problem. Everything is working for now.
Receiving is going through queueing as well. 
Coflow ordering should be working now due to back-pressure.
Increased the send/receive queue to 32 each. Note that we are counting request number not size in bytes, which could be a problem in the future.