What kind of vehicle are we talking about? The larger of the two motors would be better. The 3660. Still, these are relatively small ish motors. Not that they aren't good. For their size they are impressive. Perfect for a 1/10 2wd stadium truck. I actually used one in a small ish 4wd truggy, the HoBao Hyper TT, and it did fine, although I also added a fan. I replaced it with a full size Castle 4-pole motor and was happier with that. Hobbywing makes good products. Let us know what vehicle we're talking about and we can advise you better. But for a "relatively heavy basher", I would suggest one of their larger motors in the 540-size.