There's no doubt about it the 300 WSM is far more proven and will do everything you wanted to do, but since you don't load your own ammo, what would be wrong with a 300 win mag? You can buy ammo for that cheaper, it's been around since Christ was a corporal, and it'll do everything you ever wanted to do, it's just a plain Jane good cartridge, I know you didn't ask for any other cartridge suggestions, but that's my two cents
So whats in SC that you need a 150+ gr bullet to kill? The 270 wsm will kill anything in the CONUS with a 130 gr. And be flatter shooting to 500 yards then both the 6.8 Western or the 300 wsm. Or the PRC'S for that matter with factory ammo. The 6.5 PRC looks like the 270 wsm's little brother.
So you buy this shinny new rifle in 6.8 western but it doesn't like the 2 or 3 factory rounds made. What then for the non reloader, you start reloading or sell it? The 270 wsm has quite a few factory ammo choices and the 300 wsm has more still. If your wanting a LR target and hunting rifle, and dont mind more recoil then the 300 wsm is a great choice. It just set a 1000 yard record with a 10 shot group at about 1 inch I believe. BUT if your learning LR you really should learn on a 6 mm, like a 6 mm Creedmoor since you dont reload.
Attached are pics of a cow elk my buddy killed with my 270 wsm, 1 shot cornering hard to us at 100 yard, bullet struck at base of neck and went under hide and blew up a fist size hole and then penetrated 22/24" and stopped at the rear of the rib cage on the backside. And that was a factory 130 gr Federal Vital Shock with a Nosler Ballistic Tip bullet. Which shot .6 in my featherweight model 70. A solid copper bullet like a 129 LRX would have probably pasted through. But she only went 49 paces with a so so shot.
Also attached is a ballistic comparison of the 270 wsm and 6.8 western to 400 yards. I concede that past 650 yards the 6.8 is better, but not at a distance most shoots are taken. I read a review of the 6.8 and used the chrono data to compare the factory load against my very meek 270 wsm 130 classic hunter handload.
270 wsm 130 gr Berger Classic Hunter starting at 3089 fps and a 6.8w 175 gr Seirra TGK starting at 2835 fps. Both at 1000 ft attitude 40° 50% RH with a 90 degree FV wind of 10 mph, SC ish conditions I guess. The 270 wsm even with a meek load has 5 inchs less drop and only .5" more drift at 400 yards and about a 20 yard further pbz. The Fed factory 270 wsm ammo chrono'd at 3300 fps even, the box numbers, unusual but true. So even flatter.
IMO the 6.8 western is garbage. Designed to be the 6.5 prc of hunting, in .277 of course. But Winchester going to a smaller case and bigger bullet lost what made the 270 wsm special, its super flat close to intermediate trajectory. The increased "shootability" of the 6.8w having less case/recoil and a higher bc bullet for LR shoots only helps past the distance most shoots are taken and made the trajectory kinda meh. I shoot LR a lot, have shot PRS with my 6xc a little, and I get the concept of heavy for caliber high bc bullets. IMO the 6.8w is only good for creating more .277 high bc bullets.
For hunting if I could only have 1 rifle it would be a 270 wsm, or a fast twist 7RM. Depending on where I lived and the terrain. Look at the model 70 Tungsten. Put in a Timney and its done. But the factory trigger isnt bad.