Keep in mind when trying to hunt at long range...

Lets say you are pushing a 30 caliber Berger 230 (one of the highest BC 30 caliber bullets avail) around 2,900 fps.

If your range estimation is off by 15-20 yards, that means about a 10 inch bullet drop difference in just 20 yards.

If your wind estimation is off by 5 mph, that means a 18 inch difference.

I spend a lot of time shooting at long range, but I still limit myself to inside 500-600 yards to ensure a humane kill.