The heaviest I would use in the 308 is 175gr. You can go heavier, but it i would only go to 180 for a specific hunting round. The Army went to 220 grain for the 300 win mag, and ended up burning up barrels in 1500 rounds. Using the 190 grain more than doubled barrel life, so they went back to the 190gr. The same could hold true for the 308 shooting heavy 208gr. The 208 is more of a handicap in my opinion. You cant get the velocity up high enough to take advantage of the high BC, so you have more recoil and no long range benefit. I havent read the whole thread, but if you are shooting under 300 yards, a 155 gr AMAX will work just as well if not better.
I was shooting M118LR out to 800 yards over the weekend. I can tell you that 800 yards with 175 gr loads out a 20 inch barrel is close to the limit.