i say raptor, and not just because i have one, a good friend of mine has a 05' Z400 with a yoshi slip on and i still win in the drags. a full exhaust and opening up the intake adds 13hp!! so, in stock form they may be close in performance, but when you mod the raptor and Z400 with basic mods, the Raptor just kills it. Plus, even though their close in dragging, you can just lug the big engine around in 5th gear and have all that low end to still spin out the tires and such, where as you need to revv the z400 more to keep it in its "power band"