I have the Medusa 36-60-2200 on my Hyper 7 and it works great with 4S.

After running it fairly hard on a soccer field until the LVC, the temps were still acceptable; fyi, it is geared for about 43mph and its quite torquey.

Even if you gear it to 45mph, it should be fine since your buggy is lighter/better than mine.

I say go for the 36-60-2200, and you should be happy.