The company i used to work for had an old forklift with a detroit in it, while they were working on it she stuck wide open, not really much you can do when those things let loose.
Used pro-x in my girlfriends stock re-build, not bad at all and has been ridden quite a bit, still great compression, if im gunna add anything to the motor i will go wiesco.
are you buying a new set or do you have a set laying around. If your buying I would go for a set of snipers, shearers, or cpi's. there is a lot of threads on comparing pipes on here.