I have a DPMS .308 with a cryo'd and fluted 24" barrel. I went through a 200rd break-in (no measured groups) and started measuring groups after that. with 140 rds post break-in, I have an average of .74 MOA, all shot at 200 yards. The best 3 round group was .186 MOA and the best (of only two) five rd group of .65 MOA. I tried a few different rounds and settled on the Fed Gold Match 168gr since then. I haven't tried the 175gr yet, although at 200yds I'm not sure that there would be much of a difference. I need to make a friend in the Colorado Springs area who belongs to a club or has access to a longer range..
The information that I have gathered from other DPMS .308 owners is that they all claim sub-MOA. If you add in a few that might have a liberal ruler, I still figure that it is at least an moa rifle, even though DPMS makes no claim or gaurantee of accuracy (that I know of).
It is my understanding, as far as barrel length for the .308 goes, is that you can have good accuracy at short ranges with a 16", but that the .308 needs about 20" to burn completely. So barrels with 20-22" fare better at longer ranges due to the increased pressure. I have also read and seen that a 24" barrel doesn't have any real increase in accuracy or pressure over a 20-22". If you notice, the SASS uses a 20", but whether it has to do with what I understand or if it just has to do with the benefits of a shorter barrel, I don't know. It could be a combination of the two, that the benefit of the additional 4" is not enough to warrant the extra length and weight. I'm open for comments about this, of course. I guess that your intended purpose will determine the barrel length. I wouldn't take what I said as gospel, it's just what I have read and seen (articles, comparisons, shooting time, etc.).
I am not sure if the .308 is good for anything much beyond 1000, perhaps better for 1000 and under. IIRC, with factory ammo, 1000yds is possible but 800 yds is about the limit.