I've never shot any really big stuff with my .454 FA. Always used .475 and .500s. But, I've tested a lot of .454 bullets on deer. I always felt if a .454 bullet wouldn't completely penetrate a whitetail, then I wouldn't use it on larger game. I've dug several bullets from whitetails, but never a AFrame. That's what I'd use. The extra weight should help a little more with penetration.
Elands are big, tough animals. Dropped mine with one shot, but with a .375/.284 XP.
Kudus not so tough. Dropped 2 with 125/130 gr. 6.5/.284. Did wound my first one in 1985 at 250-300 with a .375 JDJ. Trailed him up. Did not look sick. Dropped him hard with a 310 gr. SSK lead in a RSB at 60 yds. Caliber and weight help a lot with big animals.