If it was me looking to shoot out to 300 max, I think a 22-250 would be my choice.... but IMO a 6.5 Creedmoor is better for a wider variety of target shooting if you plan to go out to 1000-1200 yards.

For shooting groups, then magnification is your friend. If you are shooting steel, then I would look for a 3-15 or 4-16, since there really isn't a reason to go higher. I personally like the Burris XTR2, but if that is out of the price range, then the Athalon Argos BTR or SWFA SS fixed 10 are great in the 300-400 range.