i maybe new to this, but maybe i'm missing something. can the MGM compro 16018 even handle 6cells (22+volts)?

6s at max voltage is 25.2v (4.2v/cell). 18 NiMH cells is just about the same right-off-the-charger at 25.2v (~1.4v/cell). So, yes, it can.

Well the controller is fine for the app, but I think the motor is too hot. I ran my 8XL on 5s (see vid below) and it was waaaayyyy too much power for everyday bashing IMO. 6s will be out of control.

I pull over 120A peak on mine w/ 4S, I will venture a guess you may be pulling 140A on 6S for a 9-10lb vehicle. I'm not even sure those batts will be up to it. If they get hot, you are pulling too much A.

Its been my experience that WOT drving keeps the system rel cool. However, once you start doing partial throttle stuff (like normal bashing) I think you will find you are going to heat up that motor quick. A fan is not really going to do jack. EX. A properly sized lipo should give 3.5V under load, so: (6*3.5V)x 140A=2900W !!!. I think a reasonable efficiency rating for cheap Feigaos is 70% (may even be high, but just watch...)

2900Wx 0.3=870W. The 0.3 (the loss to heat based on eff rating, 70% or .7)

This is the amount of power lost to heat at peak power. This is a lot. No fan is going to help you out on this. If you want to run massive power, you have to get a high eff motor like a Neu.

Also, I've found proper gearing is also key. There are times my motor was running hot esc cool ( 180F/115F), and gearing up made it run cooler and put more load on the ESC. Temps were more like 160F/145F. If you are wanting to do 40mph, then I would just use the 8XL on 4S and properly gear it and it will do 40 (if the truck is not too big) or keep the 6s and get a 10 or 11XL (and system will be cooler this route, voltage is your friend.)

for 6s and a feigao I would go with a 12xl. I use to run that on 5s(now I run a neu) and it had very good power but still controlable.

Thanks guys.

Where can you get 10xl, 11xl, or 12xl motors? RCM store doesn't seem to list them.

I dont know for sure but try unitedhobbies perhaps.