in principal I agree with daveorgan, but I tried the cheaper 50Amp Esc's and run into problems at low rpm's, they just didn't work. I would spend the extra money and buy two 25Amp M-troniks viper marine ESC's. I use them in some of my boats and they work superb. ESC's from Action electronics seem to be good too.
(the 25A version for extra reserve just in case you stall a motor)