As i mentioned, i'm using a Sightron STAC 4-20X50 MOA.
I do shoot 600 yard F-Open with it. Originally with 7mm-08AI, now with 284 Win.
Put a SIH 3-9X40 on a friends Savage 110 in '06. He loves the glass!
I just got my Field Target in today 4-12X40 MOA. This is going on my Savage 111 in 7mm Rem Mag, that i also shoot out to 1,000 yards with, just not matches.