I have both a 450R and the XX. Granted, both of my 450Rs are built up pretty well, and the XX not so much, but IMO, he wont have to do much stock to stock for drag racing. The 450s are very fast machines as they are, about 38hP stock, and they are lighter and nimbler. I race the 450s on MX, and the XX in scrambles. I tried a 450 in a scramble, but seeing that it is not my main thing that I like to do, I use the XX for sheer comfort. Both of my 450s how they are set up blow away the xx up to about 60ish (I let my cousin drag me, and we swap back and forth machines, to make sure it is just not the driver), but after 60 my 450s are about topped out, 65 at the most, and the XX keeps going. I don't have a pro strip or anything, just fields, but with the weight of the XX it def hooks up better (plus I have RZR2s on the rear versus mx tires on the Rs which don't hook up well in grass). This is just my experience, I have no idea what they will do stock to stock, but all of mine have aftermarket stuff, and this is what Im basing this on. Also, the others are right about the pull, and the fact that is fuel injected is a huge bonus, pretty much 0 throttle response time, haha.
2008 700xx; Power Bomb header with power core 4 exhaust, Power Programmer III, pro armor nerfs, prm products control front and rear bumpers and full skid, 10" ITP rears, ITP Baja's fronts, RZR 2's all the way around, Uni filter, 13t sprocket, CCP steering Damper, DS450 shock swap, Dual Gasser Throttle, bar risers and Moose barkBusters. 730XX kit plus other engine mods!