Like most of these posts, it ain't black and white, it depends....
-- on the bench?
-- practicing field positions?
-- hunting?

I haven't found my upper limit yet and whether I pursue it depends on time, money, and direction; I would consider one step further up to like a 500A2, 500Jeffrey, or 505Gibbs, but will likely work on a super 308 or super 338 for long range work before going further up the scale, asI really feel I have all I need at the moment.

I'm still in great shape physically, so there is no need to start disowning my pastin order to feel good about my present (the old "I used to have magnumitis, but now I know better" crap)....
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Have the 50 BMG and as mentioned before, it is not the recoil but the shock wave that isthe potential distractor.... it pays to blow your nose before shooting as it can literally "slap" the"nose moisture"right out of you.

Have shot the 500 Nitro Express.... not bad at all, big straight sided case and 2100 fps with a heavy double rifle.... it is a puppy dog.

The .400+ safari bolt rifles: 458 Lott, 416 Rigby, et al, are definitely not gallery guns and you'll never burn the barrell out on them and I would not shoot them prone. Barring "muzzlebrakes & weight added to stock & leadsleds on the bench;" you definitely need to be on top of your "recoil management game" when using these rifles.Only a fool uses the "school of hard knocks" training school with these rifles. There is nothing casual about them. Go for a "quality" experience, but notfor "quantity." That said, if you have the mental control, thenyou can put your shots right on the mark.

The 375 H&H is warm and cuddly and a lot of fun to shoot, and even more fun to kill with.... a hand full, yes, but very managable.... one sweet thumper. In some countries, though, the 375 H&H is not legal for dangerous game, the requirement in some places being .400 or betterplus other energy requirements.

338WinMag, 300WinMag, 7mmRemMag.... while quite easy recoil-wise by comparison (unless you put yourself in the ultralight-no-muzzlebrake situation) --- they are great tools for the right jobs though.