Depending on if the build is for Robot Wars or just an upgrade for an old HW to run at the live events, you may want different speeds, which is a pain.

I looked at these motors early on for our HW (I think at least 1 robot ran these at RW this year) - http://www.hobbyking.co.uk/hobbyking...ner_Motor.html But the Kv is far to low for your gearboxes.

There were also these - http://www.hobbyking.co.uk/hobbyking...ize_heli_.html But the 5mm shaft is pretty dubious, or the Aquastars - http://www.hobbyking.co.uk/hobbyking...ess_Motor.html wich you can run without cooling.

You may need to rely on acceleration curves to reign in a higher KV motor if you cant find a suitable lower Kv one, but that's pretty easy on the new DX6.

What size wheels are you looking at/or stuck with?