I'm dinging (donging?) a 15" gong with regularity (thanks to this forum) when the air is still at a 1000 with a 4.5-14 buckmaster. The buckmaster holds up just fine. I think as long as you can see the target and the scope holds zero and returns to your zero then you're OK. I use the mil-dots instead of turning the turrets though.
I also use a bushnell 4-12 yardage pro scope on another gun that 's able to hit the gong.
The gun is really what makes the difference as long as your scope holds still. The article I read on this forum (Long Range Hunting - LONG RANGE RIFLE ON A BUDGET
), says your gun needs to shoot 1/2 moa or better. I have one that shoots 3/4 (did better last time out though) and another that shoots 1/4.
If your gun doesn't shoot 1/2 or better, you're money will go farther by having a gunsmith work on it, instead of buying a new scope. My 2 cents.