Thanks again for the replies gents.

Normal usage will be mostly short bursts, as I mentioned before, maybe 10-20s at a time, few times a day. Heavy usage would probably generate loads of heat, so would need additional vents + fans in order to cool it down. Not sure how much heat will be generated, so it's all guesses at the moment.

I don't really need to keep 3:1, I can even use 1:1 if the motor is up to it. Steppers would actually benefit from low ratio, as they provide rather high torques at the lower speed range that interests me.

I've stumbled upon Mark's (blackburn mark) spindle thread and also discussed the details with him. I've looked at this motor:

EMP C6354 KV250 Outrunner brushless motor 2450W for RC airplane match 90A ESC | eBay

which can be ran at 500RPM at 2V (which seems oddly low), but I'm not sure of the torques produced at that point. I can also run it at 1000RPM at 4V and then use 3:1 to drop down the speed to around 300RPM.

Regards,
dsc.