With the extra speed you can go farther, but the big issue is if you loose signal things can go wrong faster at speed. If you're flying through trees - you'll need the extra power for sure. If you're flying over an open field and above obstructions between your antenna and your multi - 200mw is fine. Trees block a lot of signal at 5.8ghz so it takes a lot more punch to get through them and even if you're flying slower and can handle a short signal dropout you'll probably need 600mw to get more than a few hundred feet away.