I have a "1000w, 48V" motor that I've operated with a 52V battery (58.8V fully charged; 14s X 4.2V = 58.8). It will attain 35 mph on the flat, no wind, 175 pound rider and 50 or so pound bike) and has never come close to overheating (but I don't ride it "wide open" for long stretches). If you're worried about overheating there are methods to minimize it (see endless sphere for adding materials to the inside or of the hub to increase heat transfer.or heat sinks to the outside for the same purpose). I'm assuming you'll employ a direct drive hub, and these transfer heat effectively.