Well at 100yds the AR-15 is going to win hands down.
At 300-600, still the AR-15 goes with the blue ribbon.
At 1000, a .308 surpasses the tiny .223 round competitively, even in the hands of an experienced shooter.
If you're only shooting 600-800 yard matches though, the Bushmaster will suit you admirably against any of the other rifles for a smaller price.
By the way, nobody turns an FAL or, perish the thought, a HK91/G3/Clone into a competition rifle. The AR15 style rifles, however, are superior in both ironsight and scoped match types.