I see some slowdowns with etqw (can't test heaven) on HD4890 that seem to be caused by this. It's not constant - in fact mostly etqw with current head is the fastest I've ever seen it. It may, however, during a short timenetdemo just suddenly drop to 4fps for a few seconds, or it may start slow ~10fps then go full speed. With this reverted I haven't seen any slowdowns (yet).