[BrianG]

Don't get too hung up on the power ratings. The rating simply means it can handle 1500 watts (~2HP), but will only pull this kind of power in bursts. Just looks at most everyone's eagletree discharge graphs. 100-120A bursts are common, but the average is far less. Unless you plan on pulling a trailer where the motor will be working every step of the way, I wouldn't worry about it too much.

By the way, a motor is not a "constant power" load, so you can't assume it will pull the right amount of current to equal its rated power. If a motor will draw 107A @ 4s, it will draw more as 5s (133.75A using your 3.5v/cell example). If you want to keep the amperage at ~107A but use 5s instead, go up one wind rating (like a 2.5d instead of a 2d).