I don't own a .243 WSSM but I do have a .243 and the ballistics are almost identical. The .243 round is fine for antelope and the premium bullets now available make it even better because they have more downrange energy and stay together much better.
Unfortunately,bullet choices are limited in .243WSSM. After a quick internet search, the only premium factory load I could find was Winchester's Supreme Elite Cartridge with the XP3 95 grainbullet.(Cabela's) The XP3 is an upgrade of Winchester's Fail Safe bullet. I have not used it but I am sure it is a good premium bullet.I'm sure there are other factory rounds with good bullets out there.Of course, handloading greatly expands your choices but I am not a handloader since factory ammunition has come so far.
Good luck on y'all's hunt!