Geoff,
A boat that size, with that type of hull ought to move right along with a pair of '400's, or '380's for that matter. Naturally keeping the weight down would help, and 'ballancing' the boat (weight fore/aft) will determine if it will even plane or not.
I'm not that familiar with the '400' size motor but they can't be that different from the '380's. A pair of '380's would need an ESC that could handle something on the order of 20 amps at whatever voltage used. Most ESCs should handle 20 amps of current, but check the specs. Using an ESC that's 'bigger' than needed is preferable to using one that's marginal. (Bigger is better till you get to some ridiculou$ point.) Not sure what the current draw of the motor(s) is/are? Do a stall test on one, double that amount of current, and that's the maximum current draw a single ESC would need to handle. The size/pitch of the props also makes a big difference. So does the voltage and 'Ah' capacity of the battery. Most motors can handle a range of voltages. On the average, something between about 6 and 12 volts is most common, sort of. The 'Ah' or 'mAh' rating is another one of those 'bigger is better' thingys. Then you get to the 'is there room in the boat' for the thing? Your guess about that would be just as good (or better) than mine.
Good luck!
- 'Doc