Depending on the round, I’d feel comfortable at 1k+ if the tracking and glass is good. At 600, 10x would be a non issue.
I’d never take a shot at a deer at either of those distances regardless of magnification.
For the money, even at a premium, Razor for me. I think it’s the best bang for the buck period. Beyond the Razor you start going deeply into the law of diminishing returns.