I got my 1512/1Y today and installed it and that motor is crazy powerful. I geared it 58/20 and got the following temps after 15 minutes of hard bashing and speed runs:

ESC: 95'F
Motor: 135'F
Batteries: 70'F

I'm almost thinking I should kick it up to a 22T pinion if Neil's "Hot motor + cool esc = undergeared" is accurate. (And from what I've seen, Neil is usually very accurate) And it would put me up to about 46mph (adjusted) according to the calculator. Not that I have any objections with the 43mph I'm getting now.