For you guys shooting the CZ 550 magnums, you can seat the Barnes 450 TSX out farther, to crimp in the second groove. This gives you about 1/8" additional case capacity.
I'm loading that bullet over 72 grns. of H4895, with a Fed. 215 primer. This load is giving me 2225 fps., with 100 yd. groups averaging 1 1/2" with the open sights. Can't complain about that, and with little to no compression. The Hodgdon powders listed as "extreme" are relatively temperature insensitive, so the African heat should not be a problem, although I wouldn't let them lay around on the seat of the landrover too long in the sun.
While I have not killed any game with this load as yet, I have no doubt that this bullet, at that velocity will perform well. The .458 Win. is a very capable round if loaded correctly.
Chamber your rifle for the Winchester cartridge, and go kill something big! Good shootin'!