How high the bullet impact should be above the aimpoint, or what the magnification should be while hunting?
For the former, I'd sight in for the what should be the Max Point Blank Range (MPBR) of the rifle, which for a 130 grain SP at 3000 fps (typical for a factory load), that's a zero of about 250 yards, which puts the 100 yard impact 2.6" about the line of sight, with a MPBR of 290 yards. This is with a +/- 3" kill zone, meaning that from the muzzle to 290 yards the bullet will never be more than 3" from the line of sight. Any shot within 290 yards you can hold dead on and still hit the vital zone of a deer.
Of you're referring to scope magnification when hunting, it's a matter of personal preference, but I ALWAYS hunt with my scope at the lowest magnification. This gives the widest field of view to quickly acquire the target. If the situation warrants and allows, I will then adjust the magnification to a level that's best for the range and conditions. 3x magnification is plenty to accurate shoot shoot a deer at 100 yards, but if the deer can't see you and you want to, you can always increase the magnification before you shoot.
Mike