The VTR is a unique way to build a stiffer, more accurate barrel while still keeping weight reasonable. Taking a heavy barrel and removing some metal to form a triangle is really no different in theory than taking a heavier barrel and cutting flutes in it. I know that a fluted barrel will be ALMOST as accurate as a barrel of the same diameter without the flutes, and if done right can shave a little weight off the rifle. How well that concept works with the triangular barrel is still undetermined. But at any rate that is the why. And based on how few I've seen actually purchased most buyers are either not convinced, or the triangular barrel is just too modern looking. The concept may prove to be ahead of its time and be a great idea.
I can no longer recommend any Remington rifle, but that is another thread.
As to cartridge I wouldn't recommend 300 WM except for very specialized uses. As a 2000+ yard target or military sniper rifle they have their place. Or for someone wanting to take 700+ yard shots on larger game like elk. For general purpose hunting or target shooting out to 1000 yards there are better choices that will be more accurate, cost way less to shoot and with 1/3 the recoil.
Your first option of a 308 will work at near 1000 as a target rifle and will be effective on most game to 400. The 7-08 in theory beats 308 by a tiny amount, but ammo is less available and costs more. The new 6.5 CM does everything the other 2 do as a hunting cartridge and is the better choice as a target round. I'd look hard at those 3 and decide which works best for you.