If you are willing to pay a hefty price say somewhere between 1100 to 1500 dollars Swarovsky is a good choice as well as Zeiss, but if you want something a little tamer on the price Leupold would be my choice. I us one on top of my 300 win mag in the VXIII, not as high powered as you want but it does a fine job out to 600 yards.
I live and hunt in Arkansas and have some 500+ yard shots on my lease. The main reason I am wanting a more powerful scope is for the ability to size up a rack in a hurry. I don't always have time to use binoculars. My Leupold Vari XIII 3.5-10 works okay, but I think more power would be better for rack checking. I was thinking along the lines of the Leupold VX III 6.5-20 or maybe even a Burris 6-24 Signature Series, but eye releif is a concern on the Burris.
The higher powers are great, but the higher you go the more it amplifies your heart beat, and this translate into more movment all a longer distance unless you have or can get a good steady rest for the shot.