I have Leupolds, Burris,B&L in higher grade scopes. You might take a look at Burris Ballistic Plex which is like 3-9X. If you mount it it with Burris Signature Zee Rings and spacer kits so you can get your zero in the middle or slightly below center of the adjustment range and zero it at 300 yards and you have a hash mark 1.5 MOA below center, 4.5 and 7.5 MOA. At the top of the 6:00 duplex post it is 11 minutes which is about the come up from 300 to 600 yards for M1A and 168s & 175s.
internal adjustment scopes don't like to be stretched to the limit of their movement so if you can get initial zero with scope in middle of its adjustment range you will be much better off.
With a 300 yard zero you would be about 4" high at 100 and 6" high at 200 so hold under a bit low close in. I have two Burris Ballistic Plex and like them alot for those reasons.
I also have several Leupold Mildots but this is outside your requirements.
