Neu motor for E-Maxx

[MBX5's]

Im searching out some options for a friend running an E-Maxx (new version 3905), he's laid out a couple Feigao and looking to upgrade to a Neu 1515 Series, his set-up is as follows, single MaxAmps 4s 5000 and stock gearing, he's looking to obtain longer runtimes and not overly concerned about speed, and like to keep the temps down, it's mainly his bash set-up. Any thoughts on motor choices and or gearing changes to help reach his goals? Also wanted to add he's using the Mamba Max ESC.
Thanks