half_inch_group --
First of all, I've been using a 7mm Mag for over 20 years and haven't had a problem with wasted meat. A shot behind the shoulders does it every time, with little waste -- even at 100 yards or less. Higher velocities demand more controlled expansion which generally means a better quality bullet. A bullet designed for optimal performance at .308 or .30-06 velocities might well act more like a varmint bullet a .300 RUM velocities. Choose you bullets to match your cartridge.
Second, I LIKE the magnums, even (and perhaps especially, due to case design) the new Remington Ultra Magnums. Wish I had the funds for a .300, .338 or .375 in a RUM -- I could always load them down if desired...
Hunting big game in Colorado, the vast majority most of my shots have been under 200 yards. But you get the occasional shot where the "reach out and touch" of a flat shooting magnum is welcome.
To answer your questions, I hunt elk every year, deer and antelope when I can get a tag, coyotes and prairie dogs year-round. Next year I hope my 3 preference Points will ensure I get a bear tag. The longest distance I've taken was on a coyote at just under 500 yards, prairie dogs at 400, elk at 350, antelope and mule deer at 300.
Ruger 7mm Mag for everything at one time or another. My first and for may years my only centerfire rifle. Very effective on elk with 160g Speer Grand Slams.
Marlin .45-70 for elk, deer. Because I can. More or less limits range to 250 yards, and only that far because I use a range finder.
Marlin .375Win for elk, deer. Again because I can and I enjoy the rifle. Limits range like the .45-70.
.257 Roberts for deer come December (first year I've had it), antelope in the future, and coyotes and prairie dogs when I can find them. Low recoil but +P 115g Barnes TSX loads at 2958fps make it a formidable weapon.
.22.250 for varmints. Very low recoil and lots of "reach out and touch", especially when shooting 40g Nosler BT's at 4050fps...