An 8.5 on 3s is no worse than even a 5.5 on 2s as the rpms will be similar. Actually you could probably get away with running an 8.5 on 4s as rpm will still only be comparable to that of the 3.5 on 2s. Look at the kv charts on novak's site.
Check out my custom converted 8ight:
Sub 7lb, lowest CG of any 1/8 buggy