I shoot 175s anything over 600 yards in my SR90 .308 sniper rifle. The 168s are just too light to keep supersonic over around 800 yards. Depends on muzzle velocity, weather conditions and barrel, of course. You'll probably get keyholes if you try to push the 168s to 1000 yards.

Actually, you'll only know if you try. The numbers can be crunched all day but all of the factors in your situation will be the deciding criteria.

Let us know how it works!