It depends on which M1A you choose. Bear in mind, I'm assuming you have good shooting fundamentals locked down. If you get a 22" Standard, a 1-6 or 1-8 is a good solid choice. If you get a Loaded or National Match, you can go a little crazy with the optic. The old adage holds: aim small, miss small. If (God forbid) I find myself aiming at a human being at 800 yards, I'm aiming for one of the buttons on his shirt. To do that, I need to be able to actually see it. A Leupold Mk 4 in 50x is awfully nice for that kind of shooting. Also bear in mind that light gathering ability is never a bad thing, which is where really big expensive glass shines. In the end, it all really depends on where you are as a shooter. Most rifles these days are more accurate than the people squeezing the trigger. If you still get confused making scope adjustments at longer ranges, there is probably no great wisdom in you spending $1,000 or more on an optic, no matter what rifle you're putting it on. In fact, you need to learn irons first. For most of you, something like a Vortex Strike Eagle or Sig Tango in either 6, or 8x is about ideal for this kind of rifle.
