Man I love antelope hunting. Terrain will dictate average shot distance, and terrain varies widely, so plan on being proficient from a variety of shooting positions.
The last antelope I killed was just over 100 yards in waist high grass. My buddy had a bog pod with him and that was a crucial piece of equipment to make the shot the buck was giving me. When he crested a rise he was at 250, which is too far for me off-hand, and the grass was to long to shoot prone or seated, but on that bog pod I could have dusted him at any point if he'd have stopped. Was standing at a low crouch.
If you're proficient out to 500, I'm assuming that's prone only. Getting proficient inside 300 from all sorts of funky positions will make you a more effective hunter for sure, especially in the sage, grass, brushy country speedy bois can end up in.