Hamid the pic I am showing was for the heat sink on the ESC. That is kind of a older pic as that motor was a 3900 )with a 10t pinion) which is only 26 mm in dia.
I did the same as you did on the 3800, shaved the base of the motor as it is not cut at an angle as most motor bases are and I didnt want to cut into the frame at that point. Also I run a extra motor "Pad" to raise the 3800 motor up a little higher on top of the Extreme mount. For the pinion I just position it a little further down the shaft to make full contact with the main gear.
There are a lot of variables for heat but with that 10C batter and considering the motor can pull about 20C you will find a larger C battery will run considerable cooler. I notice that my older 1500 mah 15C battery runs a little warmer then my 20C-25C 1500 mah battery but I am measuring heat with my fingers (1 is room temp 5 is warm and 8 is OUCH damnit! anything over that is a juggleing act).
I think somewhere I said that I run a ESC that has a built in UBEC and it barely gets warm to the touch as most heat is generated by the BEC side of the ESC dropping the voltage down to the 5 volts.
BTW nice job on that motor mount. Maybe you could make a full size templet of it and post it on a thread titled "Motor mount" so others could make one.