If your talking MGs and Cannon, then an easy rule to rember is, in Aces High, they can be dangerous out to ~800-1000 but alot more effective if fired at less than 500, preferably under 400.
as for rockets and bombs, they're effective no matter what distance you fire em, its more a question of getting them to hit what you want.
Buff MGs and GV MGs tend to have about 30-40% extra range. Flak can hit out to 2k or so.