Might be worth looking at large scale RC helicopter motors. These are kind of the best of both worlds, with good torque (they're outrunners) but fairly high KV. They tend to be compact but have substantial heat dissipation ability. Not cheap but if you wait for deals and scan Ebay from time to time you can normally score big brand gear at good prices.

This is one of my 800MX 520kv Aligns with the shaft replaced. The stock shaft is fairly useless (pictured to the right) but it's 10mm diameter inside the motor, and replacing is easy enough if you can get the shaft out of the endbell. Mine needed a proper press, the press fit is impressive. These handle 12s and several thousand watts.



Edit: shown here with its full support jacket: http://i.imgur.com/WEmxpCa.jpg