Remington seems to have dropped their custom shop, which is where their safari line lived. With it went their .458 win mag and their .416 rem mag. They have made a commitment to their rum line, which runs up to .375 RUM. I'm not sure *I* like the direction Remington is going, but then, they're trying to create new differentiation in the market.
A few years back, big bores were all the rage. It looks like the SAUMs, WSMs, RUMs, etc, have displaced all that for the time being. Many of the .458 win ammo lines have been dropped. SOME of that could be coming from reports that the standard fmj's were not performing following drilling through bone. But I think it is broader-based marketing: they're now marginal sellers, and they're trying to push their new lines which they hope will be a little hotter. I'm still finding bulk winchester brass for .458 underprice, but it won't last [and hasn't; winchester still has the best deal]. At the same time, I'm still seeing components for these calibers. But they're rapidly getting pricier.
Putting 400 grain against 400 grain, I see very similar exterior ballistics between the .416 rem and the .458 win. There are 300 gr bullets in .458 available, but their secional density/bc do not perform as well as the .416 in that weight. In this way, the .416 may reach into the upper range of the .375, but doesn't really span the range of the .375H&H to .458 win. The .375H&H actually shows much greater range of projectiles, with pretty good exterior ballistics, through larger bullets on big animals. The .375H&H actually has a purpose on the NA continent, while the .458 win, though flexible enough to range from .45-70's through more than you need almost everywhere, has sacrificed most of its exterior ballistics for terminal ballistics.
A friend of mine shot my .458 win, with 2 past pads... pretty comfortable to shoot that way. You get a mighty shove: lots of exuberance, lots of rambunctiousness, and the slug smacks the target with the archetype of authority. My friend just laughed and laughed: very much pleased with the experience! Like a Walt Whitman poem packed into one moment of recoil.
Dan