I've been using the powerflex in the front lower control arm rear bushing spot and they work fine. Just pulled them out and cleaned them up a few weeks ago - look like new. I'm running the M# RTAB bushings with the GC enforcers and they seem nice and tight.
I also have UUC bushings ready to go in the rear sub-frame. Not installed so I can't say how they run yet.
You might want to check out the UUC products in addition to the Powerflex.
2002 540i M-Sport