RE: 7mm vs 300 WSM
Of those I'd definitely pick the 300 WSM over the 7mm WSM without a second thought. The 7mm WSM may shoot a tiny bit flatter, but not enough to really matter, but the 300 WSM will carry more energy to the target at all reasonable ranges. A second reason is that of the "short mags" the 7mm WSM never cause on like the 270 and 300 WSM. A lot of manufacturers who have several rifles chambered in 270/300 WSM aren't chambering ANY in 7mm WSM anymore. This lack of popularity, of course, means that ammo makers don't make as much ammo for 7mm WSM so it's more expensive and harder to find. As for the 300 WSM suddenly disappearing, I wouldn't worry about it at all. The 300 and 270 WSM's are most definitely here for the long haul. I've noticed at all my local gun dealers that they keep very few new 300 Win Mags in stock anymore and those collect dust, but the 300 WSM are plentiful and the guns fly off the shelves. Maybe the 300 Win Mag is slowly on the way out?
Mike