Most of the guys I know who race 3.2+ motors use the Chinese manifolds with great success. I used a pair on my 3.4 street boxster and love them. For my 2.7 rallycross boxster I used 997 exhaust manifolds and love those too. You need some fabricating skills to make those work though. I go over the 997 manifolds in this thread.
http://986forum.com/forums/show-tell-gallery/73877-6-months-live-build-thread-2.html