Do you have a tripod and gimbal mount? Do you have a monopod? You're probably gonna need them for the 400 2.8 or the 600 f/4. Given the choice, I'd probably take the 500, because it's something that I could still reasonably use handheld, but it wouldn't suck too tremendously with a monopod and flash for night sports.
Gitzo 1327, RRS-55 ballhead, will get a wimberely or somehting if needed.
400mm F2.8 IS USM

