Well, if all you plan on doing is shooting around that distance, you could probably save yourself some money by going with a .223. It'd be cheaper to shoot, and would carry just fine to that distance. If you decide to go 700-900+ meters, I'd probably stick with your original choice of .308, especially if you ever decide you want to kill something at that distance and not just hit it.
What kind of groups can that DPMS pull?
I've been eye-fucking a Fulton Armory for awhile now, but I just dropped $1,500+ on a new .308 bolt gun, so I've got that to satisfy my .308 tastes for awhile.