I have been running a 3905 on a Medusa 36-50-3300 on 14v 15/68 gears. Mostly through grass in my yard. Top speed was radar gunned at 42mph through grass(kind of long at the time) I get about 10min run time on my packs and motor temp has always been under 130f(heat sinked but no fans).

Seeing that you dont need 42mph maybe a Medusa 36-50-2200 with a 17t pinion might be a little nicer choice than the feigao. It is a bit more expensive but mine seems to out perform XL Feigaos at least in top speed and temps from what I have read and the vids I have seen(hard to judge by a vid) but here is mine anyway;) http://s287.photobucket.com/albums/l...rent=Movie.flv

The same motor would allow you to run up to 6s lipo if you ever decided to upgrade, just regear to get the speed range you want(14t for 6s LiPo). With the speeds your looking at you could even go with the 1/8" shaft version to use stock pinions and it's in stock right now, mine is the 1/8" shaft version also.