In WWI, when those men going "over the top" got cut down, most of the time it was by something called "the Devil's Paintbrush" - machineguns. Most of the killing power in a squad is in the SAW. Most of the men who died from gunshots (as opposed to arty) in WWI got those from machinegun fire...*accurate* machinegun fire, which is a whole different animal from accurate rifle fire. Lessons learned from WWI resulted in a lot of innovations, like issuing lots of mortars and grenade launchers. Indirect fire from a distance being the best way to counter machineguns.
Now when those men got in trenches, it sure as hell wasn't accurate rifle fire that everyone wanted, it was grenades and submachineguns. Explosives and high-volume close range firepower was the key. I'd sure as hell take a 'trench broom' over an Enfield in that situation any day....
Accurate rifle fire is very important, and can be much more so in a situation where you lack support, such as the early days of the Mujahideen in Afghanistan versus the Soviets. Crusty old bolt-action Enfields ruled in the open terrain of Afghanistan against the AKM. Some Spetsnaz units tried to issue SVDs to as many men as possible to counter that advantage. But eventually, the Mujs got ahold of heavy MGs, mortars, RPGs, and other dandy weapons captured from the Soviets. That changed their behavior quite a bit, but the essence was still there. Even an AK is deadly at range in capable hands.
The 600m .308 vs. AK scenario is unrealistic. Any army worth its salt would have little trouble finding cover and a) moving to close with that unit, b) withdrawing under fire, or c) hunkering down and calling for support. The best bet for those marksmen with the .308's would be to inflict as many casualties as they could before the targets found cover, then fade away. Against a competent adversary, you're not going to win with marksmanship alone, but it sure doesn't hurt....
I'm not sure what AKs you guys are using, but I've never had any trouble hitting a man sized target out to 200 yards with my old MAK-90, and I was deadly to paper plates at 100 yds with my friend's MAADI...unless something's really wrong with your rifle, it sould be capable of combat accuracy out to 300yds. Maybe you've got a SAR with canted sights or something?