Are you running a single 4S pack or two 4S packs? I ask because on a single 4S pack and a 7XL you can overheat the Lipo pack at towards the end of the run. I know this from experience. I've puffed a couple of doing exactly that. so if your running a single 4S, do like Sleebus says I would go with 10L, 8XL or even 9XL. If you are running two 4S packs I think you might be able to get away with a 7XL, but even so, I would still recommend a 8XL. It is worth it to get the right motor so you don't have to spend a lot of time and money messing around with gearing, fans and ultimately other motors.