Personally, a 36-50-3100 on 3s would be the best option. The 60mm version would simply be overkill unless you plan to gear really high. I run the 36-50-3100 on 3s (Elite 3300mAh 30C) and it stays cool no matter what with lots of power. Let me put it this way: I need a new lid from it being worn down.
I'm geared for around 30-35mph, which is plenty for off-road running in this little thing.