Heat isnt normally an issue if you gear it to go no faster than you would expect the nitro to go. But once you start gearing her up to go-fast mode, then even with max airflow, cooling fans on the speedie, and even heat sinks on the motors, (if the kits allow you room to fit them) then heat will be a problem. Just for the record the 3.5 and 4.5 seem to run hotter. I guess thats 'cause they produce the mega power. As we all know power means heat. I've cooked many, be carefull and enjoy.
Just as a footnote; If you run brushless with NiMh, although power will suffer a little, the system will run cooler.
Power draw I guess, but Lipo is the only way for Max Power..... Grunt.