Ahh, thanks for the help there everyone! It definitely sounds like a complex subject... The Boschs do sound like a good choice then, in that case! The brushless outrunners I thought would be best for a drive would be those NTM 50-60s (the ones that are rated to something insane like 3000w in a motor that's only about 500g) but if the torque isn't at a constant, I can certainly see drawbacks with using them, and what you'd gain in a weight reduction from the sensorless ones you'd lose in the huge gear reductions you'd need...

And Nick, thanks for the link too, I shall give that a good read!