You do have a point about the matches, Ive never been in an official one.
Its also true that it is extremely difficult to hit fast moving targets; an SAS officer stated that it could take as many as 10 rounds to hit a fast moving man at 100 yards; however, .223 has already begun to drop off at 200 yards, whereas .308 is still pumped. If your using your 10 inch abortion, your shots wont have the necissary velocity needed to reach even that far.
Besides, if you set up at night, and your opponent does the same, he'll win, because if he has any sense, he'll be outside of 300 yards and your ammo wont touch him. All he would have to do is glass the area and shoot you. As simple as it sounds. You wouldnt be able to shoot back and you wouldnt be able to run for fear of exposing your position.
Having said all that, since your shooting in daylight, muzzle flash isnt an issue, and noise doesnt really apply anyway since everyone will know whats happening once the shooting starts anyway, so thats a moot point.
Your comments on bolt action rifles are redundant. A good bolt action rifle handles the elements better, has a faster lock time, and stays effective much longer in harsh conditions than an AR variant does.