Re: scope for 600yd big game rifle
I have one of those scopes and it is superb. Perfect for hunting out to 600. Incredible optics, built like a tank, excellent turrets, have the GA reticle which works perfectly with my .308 ammo. You get what you pay for, this is a fine optic. Also have the NXS equivalent, it is a wonderful scope but suffers a bit in poor light. Might also consider the Leupold MK4 MRT 2.5x-8x - in my opinion this is one of the most overlooked long-range scopes on the market. Fantastic scope for the money.
I agree that a bit more magnification might be nice in really long shots but 8 or 10 will do a fine job on deer out to 6-700 yards.
Good luck with your decision. Owning a USO, S&B or NXS gives a special bit of pride, as well as incredible performance.