for most who shoot a 308 will say ( go too a 175gn bullet for 600 out )and I will be one to agree with that.and if you really want to go out their I would even go with a 208/210 bullet useing R17.but this is something I choose to do.its just that the 168 tends to lose everything it has out past 600.so the 175gn bullets and up take care/over from their.you start to get a better B.C. with the heavier bullets because of it being longer.so they fly buck the wind better.and that most who shoot a 308 shoot them out to a 1000 for matches.
forgot to say that even some will say to go to a 155gn bullet.but most who shoot a 155gn bullet like to push them very fast to shoot at 1000 yards.and I hate pushing bullets that fast.rather ( Lob ) a bullet to the target than burn out a barrel.again the 155gn bullet is a longer bullet in design so this allows it to buck the wind whille haveing a higher B.C.
hope I was able to help you out.my #1 and 2 bullets are the 168 and 175gn bullets.but for a long range kill or shoot on papper I love the 208 and 210gn bullet.and that its great to see a 308 be able to shoot a bullet of that weight with great accuacy.