This is a seriously jacked up question. In all honesty, not to be rude, but several facets of the question make NO sense. You're asking about short mags vs. long mags. Which is slightly different from asking short action vs. long action, in a vacuum. Then you're asking about what caliber for hunting AND target shooting. Two different questions. And then you don't include very many choices at all, and one of your choices (.308) is not really a magnum in any sense of the word, either long or short. Plus, I disagree with the oft-claimed allegation you repeat here that the 7mmWSM and .300 WSM beat the Remmags - I don't believe they do. They can match or almost match the traditional long mags in light bullet weights with the advanced powders they use, but on the whole, they are well behind the traditional mags in ballistics. Now the .270 WSM does indeed best the .270 win by a little bit, without question.
I'm afraid we need to kill this thread and start over with a new poll, by asking a question with a more narrow focus, so that it can be answered/addressed.
What are you trying to do? Hunting? Hunting what? I try to go with the smallest caliber that will work extremely effectively for the game in question, so as not to overkill on recoil, noise, ammo cost, and barrel life. Target shooting? In that case, the answer is going to be 6.5-284, since there are (a) several accurate platforms and custom barrels for the caliber, and (b) very good quality brass and bullets available from Norma, Lapua, Sierra, and others.
A good case can be made that the .270 WSM is the ultimate long range hunter round, arguably, since it's somewhat light recoiling, yet uses a large enough bullet to take down largish game such as moose, and it's about as laser-like of a trajectory as you're going to find. You can extend your PBR out to 250 or even 300 yards, depending upon game vital zone size. But I still wouldn't get one over the .270 win because the ammo is much more expensive, and it's gonna be more of a barrel-burner, and the .270 win will EASILY do everything I want it to do and more. I just cannot imagine ethically taking a shot past 250 yards - too much risk of missing - I'm gonna wait and get closer or let the game come closer to me. Well, the .270 win is very laser like to that distance anyway, so why go any bigger/ faster? The 7mm maggies are also a nice class of large game, long range rounds, but (a) they start to beat you up a bit more, and (b) I'd go with the traditional 7mm Remmag any day over the 7mm WSM. As for .300 mags, man that's just way overkill AFAI am concerned, unless maybe hunting goats out in the some high barren mountains where you cannot get any closer than 350 yards without the goat seeing you.
Reminds me of a few years ago, was hunting with this guy who was using a .300 Weatherby mag turnbolt (Weatherby of course). We did a drive, and jumped this tiny little mountain-country doe (couldn't have weighed 70 lbs), and he's shooting at it - twice - on the run. He misses - I couldn't help but think of the absurdity of the overkill there. Don't matter how big the caliber is - it ain't gonna help you make a hit.