I've used nitro from 20-40 percent... nothing breaks or anything when you change it, but youll have to change your tune and thats about all. id just stick with 20% its not really worth all the effort. 20% will give longer engine life if you're just bashing around.... and really the race is kinda silly. big block vs smallish block. DEFINITELY VIDEO it tho... i want to see some real footage of a 3.3.
the 3.3 really isnt much smaller then a big block. its .20 compared to .21, and with the smaller engine size overall and less weight, it might help you out.
.21 conversions in tmaxx's also always take some time to setup right. if you get him while its still pretty fresh, id say he'll break off the line or before the race starts, or his tune wont be good enough for max power.
if i were you, id throw a pipe on it ASAP, and a big motorsaver filter, and get your carb settings dialed.
if the mid range is as sloppy as some people are saying, you might not need new gearing at all, if you can put a gap between you and him before you both reach max speed.
i love the rivalries that have come with the new traxxas rigs. revo vs maxx , jato vs rustler... I'm jazzing up my rusty now to try and smoke some jatos.