[highflier]

I think that is a tricky question to be asked. Alot depends on performance you want.

I personally find 1000watts to be a good starting point. Others will tell you more or less.

5s= 18
6s= 22

1000/ 5s = 55amps
1000/6s = 45 amps

now if you want a 2000watt monster.. just double the amps.