[lincpimp]

For 20+ lbs I would suggest going to a 1527 motor.

A 1200kv motor will put you around 53000 motor rpm. That may be too fast depending on the gearing you can fit and the speeds you want to run.

A 1000kv motor will get you motor rpm around 45k. This may be a better choice, depending on your gearing limits and desired top speed.

Looks like a 1527 2D at 1150 kv would be a decent choice, or a 1527 2.5D at 925kv.

I really think a 1521 will be stressed too much with this setup.

There may be other motor choices out there, suck as a suitable leopard motor perhaps? I would stick with a 4 pole motor, as you want more torque.