I agree that 7500KV on 3S is way too high, on a jet it will hardly work up to one third throttle, or am I mistaken?

Did you read this, on the eBay add:
When using 9-12cells NiCad(NiMh) or 4cell (14.8v) lipo, you must disable the output of the built in BEC and using external UBEC device to power up the receiver and servo.

Running 3S you're on the edge and you may cause the BEC to overheat, adding that to the ludicrous rpm's (for a jet/boat) the motor is capable of, I have my doubts if this ESC will play along...

Regards, Jan.