RE: Overkill?
The .243 will kill the antilope just as dead as the .300 win mag will at 300 yards. I've shot and hunted whites with both. I would go with what you're comfortable with. My cousin hunts deer in kentucky with a .300 and only will use the .300. He says that when he shoots he doesn't want any doubts about whether or not that deer is going to go down dead. I used to hunt the same area with a .243 and killed quite afew deer with it. Doesn't hurt the meat that much. Neither one has what I would consider to be an unmanageible amount of recoil. Although I won't even pretend there isn't a difference. The ammo is priced comparibly. So go with what you're comfortable shoot. Here is a tip. Find out what you're average shot may be and then that will give a better idea of what you shoot use. While a .243 would be perfect out past 200 and even 250. The .300 should give you flatter groups at longer ranges.