Although as yet I've had trouble getting any RC5-72 packets down. Not sure why.

Two reasons I can think of. If your going through an older personal proxy, it might not have RC5-72 blocks.

Second, if you simply upgraded your client executable without redoing your ini file. The default dns names of the RC5-72 network are a bit different. The old network had v27 somewhere in the name, the new one has v29.

I've got a few of my machines updated so far, but am holding out for better performing cores before I update some distant clients of mine.