Goat,
there has been many post about pipes on these forums. As you can see from my Sig. below, I am a little BIAS to the Thunder Alley System. I race here in California and ride a 2-smoke. I am getting blown of the track by the bikes running the Thunder Alley. They have a different sound to them and you can hear them coming. I just usually move out of the way because of the roost I know that I am about to get. Two of our local pro's (David Boothe and Frank Darnley) swear by them. The only bike I have, that I run the pipe on, is my sons XR50. So, I can only tell you what I see and hear.
I would say that 90% of the thumpers here run the
Thunder Alley system. They are happy with the low to mid range power it adds to their bike. If you do a search in the forums, you will find many testimonials about the TA system. I will be getting an '03 CRF450 in about 3 weeks. The first thing that goes on the bike is this system.
By the way, I only built their website. I have no other interests in the compony. I only built their website because of all the positive things said about the pipe. I met Bob and could not believe how cool he was. He stands behind his product and will work with you, unlike the "Big Companies." I think customer servise is almost as important as the product you are buying. You can click on the link above to check out the pipe.