I guess it depends on how the game is scored. Is accuracy more important than time, or vice versa?
I know the internet will swear up and down that ARs will have no problem consistently hitting a 1" square at 300 yards, but relative to bolt guns they've always lagged way behind in the accuracy dept for me. Hell, even in dead calm conditions only the best bolt guns are going to be holding a 1.5" circle for 60 rounds; my last 300 yard tourney nobody shot a 600. Several scores in the 580s. If the game weighted towards accuracy, I'd be running the a .308 bolt gun. Probably work up a load with 155.5s (which should be stupid easy to find a load for) for minimal recoil.
If it's weighted more towards time, then I suppose the AR would be the ticket. Of the ones you've got, I'd be shooting whichever one is the most consistently accurate. Unless you're shooting in hurricane level winds, the wind isn't going to be a massive factor at those distances. If .223, shoot the heaviest bullet that's accurate.
My 2c.