I've been thinking about acquiring a new rifle in a "magnum" caliber. I'm not anticipating winning an all expense paid African Safari or having sudden polar bear invasion down in Texas. It's just an idea I've been toying with for a while.
I've always wanted a "belted magnum" since a stranger I met at the rifle range in my youth let me fire his .458 Win Mag. Damn near knocked 12 yr old me out of the chair and kicked like a mule...I couldn't get the grin off my face for days. I realize that the time for this technology may have come and gone or at least is passing by. This type of case certainly isn't a requirement.
In any event in my research I keep running into roadblocks of one kind or another that keep me from settling in on the definitive choice.
.375 H&H - cases and dies are hard to find but keep coming back to this one.
.338 Lapua - way to expensive for a pinch-penny miserly man such as myself.
.300 Win Mag - Hmmm... possibly but does it have enough attitude to really shine vs .308
.300 RUM - Horror stories of it being a barrel burner <1000 round life
7mm Rem Magnum - Flat trajectory like a .270 but comparable energy to a 30-06?
Lots of others that give me pause due to availability or just plain lack of knowledge...338 Win Mag, .300 Norma, 416 Rigby.
Lost in the data.
.40
I run four catriridges you list (.375 H&H, .300WM, 7mmRM, .416 Rigby), plus 3 additional magnum rifle cartridges - 7mm WSM, 325 WSM and .264 Winchester Magnum
The magnums really split into 3 categories in my mind:
1) Plains game/thin skinned non-dangerous big game cartridges - basically "elk guns". The 6.5mm, 7mm magnums and .30 magnums (with a couple specific bullets) really shine for this. They let you build western hunting rigs that buck the wind like nobody's business and extend the distance you can shoot in any given conditions by maybe 50-200y depending on what you're comparing them to. They do not have any particular "thump" factor - kicking a little less or a little more than a .30-06. They benefit from big optics edging into "tactical" territory. I own and have hunted a lot of these, and the 7mm WSM shooting 175gr A-Frames is where I landed as the "best" at least for me as a reloader and wanting a light rifle while maintaining pass-through terminal performance from the muzzle to long range. There are also catridges that are not explicitly magnums like .280 AI that fill this role.
2) "Crossover" magnums that offer both some long range capability and some bear/thin skinned dangerous game stopping capability. This is basically the .358 Norma Mag, .338 WM, .325WSM, and 8mm Remington Magnum. Of the three, the 325 WSM is the one I use for weight reasons more than anything else. But it's not super well supported. Not bad, but you'll probably form brass from .300 WSM. The 220gr A-Frame is my preferred bullet. This rig has less reach than category 1) but more than a dedicated stopping rifle. The .375 H&H with 260gr Accubonds is probably the biggest rifle in this category. You probably want a CRF rifle with a high-reliability open trigger here.
3) Stopping magnums suitable for stopping thin skinned dangerous game, and at least some capability on thick skinned dangerous game. The .375, .416, .404 and .458 magnums all fall in this category. My personal preference is for the .416 Rigby. You definitely want a CRF/open trigger rifle here in my opinion. No point in toting around a stopping rifle in an unreliable configuration. If you want thump, this is where you get it. Some like the .458 Lott and .416 Rigby may have more thump than you want at full power. On the soft shooting end there is the non-magnum 9.3x62 that's the lightest rifle you can use for dangerous game in some places.