If you want to go as fast as possible, go w/ the HPD race pipe like the old FTR style that doesn't burn your leg w/ the appropriate clutching. This thing will scream w/ this setup. I used to have the HPD trail pipe similar to the Ritter pipe etc but this race pipe is a huge improvement over the trail pipe. It's a screammer especially w/ the lightened flywheel. Yes I can still putt around all day long w/ it too. It's tied w/ a modified Banshee up to 5th gear on a road drag race, to give you an idea of the speed.
Jim Maloney 98 400 Scrambler

 

A lot of people go with the HPD for the scrammy...which works nice if you add a clutch kit...I have a supertrapp for my 500 and I like it a lot...I have the race core which gives good power gains and it sounds really good..loud but not to loud...or you can get the quit core..

 

Any opinions on RcR top end pipe

 

The RcR top end pipe is said to be like the HPD trail pipe. The only thing negative I've heard about the FMF pipe is that the welds tend to split. I knew a guy with one and it sounded really nice but not sure how it performed. I'm an HPD/Ritter man myself.

 

Try a White Brothers slip on i put one on my scrambler and it run's liked a raped ape. I did not have to jet and I got a lot of power out of it