Originally Posted by subyswamper
P&P the stock manifold and buy the grimmspeed cross pipe.
I would have to agree with this. Although, my only experience is with the GP Moto UEL headers and they are more trouble than they are worth. Lots of rattles/buzzing even though everything is tight and wrapped and I haven't seen very much to prove they do a lot for these motors. That said, this is for the one set of headers on my motor so I can't really speak for others.
There are quite a number of threads around this topic. I believe some even have some dyno numbers.
I got mine dirt cheap which is the only reason I put them on. I will probably be switching back to the stock manifold soon.