hmm iam gettings render speed problems too after installing SR3.
Mainly even though ive choosen 4 threads only 2 of my procs are used (using alt-ctrl-del) and only at 15% CPU usage!!! (before i was getting a 90% CPU usage from all procs). I tried playing around with the adaption Threshold and memory limit buffer but very little difference. it takes me now almost twice as long to render O.o !!!