runtime vs power

I don't know what metalman is running his 7XL in, but I am running one in a buggy conversion with a MM on 4S and haven't had any heat problems, although I am running a 30mm fan on the MM and a 12v 40mm fan on the motor. The combination in a buggy EASILY does 40mph. I'm almost sure that an 8XL will be able to attain that speed, though you'd probably have to work with the gearing. I'm thinking of getting an 8XL for my buggy for the sake of gaining runtime. With my 7XL and a 14T pinion, I've done a few practice runs with people that happened to be out at the track and so nothing has even come close to being able to keep up. I think that I can afford to sacrifice some speed for more runtime.