I just stumbled across this thread after working up handloads in a .458 Winchester Model 70 for an upcoming safari.

Without excessive pressure I can get 2200 fps with Barnes 500 grain monolithic solids and 2300 with Barnes 450 grain solids. 450 grain TSXs and 450 Grain North Fork solids get about 2275.

Ths secret is to use AA2230 powder, which is denser than H4895, although the slightly reduced velocities I get with H4895 would be satisfactory. These loads are compressed very little if at all. Personally I am going to use nothing but AA2230 for my .458 hunting rounds except to use up the H4895 on 350 grain Hornadys for practice.

.450 North Fork solids are said to penetrate better than 500 grain round noses (though the Barnes 450s have a 7mm flat meplat vs. 8mm on the North Fork). Energy is over 5000 foot pounds. The 450s recoil noticeably less. I see no reason to use a Lott because I appreaciate the short bolt throw.

As for sensitivity to "the high temperatures of Africa," it gets hotter in Ohio in the suimmerthan in Africa in the months I hunt.