I have a 400ex. GREAT 4 wheeler. I have several mods as well. And twin cams are good, but you will never put out as much torque as a single cam. Im looking at a turbo kit for mine now. Nitrous is getting old. I have a 12:1 compression engine, bored .80 over, head ported and polished, hot cam, over sized valves, extended rev box, racing ******, racing clutch, 50 shot right now, white bros exhaust, bigger carb, and couple other nick nacks. I play in sand and at drag strip. If you want to go in mud at all and plan on getting in deep @ss mud go with 4 stroke. 2 strokes are pain in the @ss. If you want a nice light 4 wheeler thats quick get a 400ex . Stock to stock raptor 660R and 400ex is bout the same. 660R to heavy.