one pipe that i think is good is HMF... 6-9 hp on the 450 and thats just the slip-on.
my buddy put an mbrp on his pred... i dont like it at all... doesnt sound good... doesnt add much power.. the opening in the silincer is only at the most 1/2 inch around.. i was like wtf.
big gun doesnt make a bad pipe, i dont think...

 

DEALER cost is 5825.00 and the bike has 186.00 dealer holdback

 

the best pipe i have found so far is the ron woods racing complete system and it comes ceramic coated and looks great also the headpipe is huge.