I have recently made the switch from OS to RB Concepts and will say without a doubt their engines far surpass anything else i have ever raced with. I currently use a Rody modifed V12 in one of my touring cars, here is a link:
http://www.unlimitedengineering.com/...ml?id=XMxyGLkw
I also have a Rody dyno's C5 on order as well as a std C5