I am looking at purchasing a slip on for my 2014 YZ450F. I am a novice MX racer just looking for an exhaust that looks good and has a bit more aggressive sound. I have narrowed my choice to three different models:
1) Yoshimura RS-4 Aluminum slip on.
This one is the cheapest ($315 is what I found), has a carbon fiber end cap, and looks fairly good in my book.
2) Pro Circuit T-6 Slip on. This one is just aluminum and stainless (can buy carbon cap separately for $100). Best price I have found $395.
3) FMF 4.1 RCT SL. This is the one I am leaning towards most. It goes for $404 and has the carbon end cap.