from the sound of it, your friend wants basically a motor that is what many would call "too much".
in that case, the best motor for that situation would be the castle creations sidewinder sct 1410 3800kv motor. it can handle MUCH more than the stock motor and if he wants a better esc along with it, that motor can be bought (at a better price) with the esc. i use that specific combo in a much heavier vehicle than the rustler and it handles it very well.
there are plenty of places to buy this motor/esc combo. this link is just an example of the combo i am talking about.
http://www.castlecreations.com/produ...inder_sct.html