I'd have to agree with Sloth. I have two different 700s in .270, and have shot or own about 15 700s. Not one, NOT ONE, ever had a problem with accuracy.
As for your question. The .300WM is a bit over kill in my opinion for just deer. If you intend to hunt larger game someday then the 300 will work well for you. Just remember the 300 is going to kick a heck of a lot more than that .270. I have killed many, many elk with a .270 and never felt under gunned. I have several students in class that shoot the .300WM. Many, have problems with accuracy because of the flinch they develop. They make fun of each other.
As long as you are considering a larger caliber why not try the .338WM. It has more energy, shoots as flat with a heavier bullet, is accurate, and kicks about the same. If you reload, you can do some great things with this cartridge. You can load it down with even 180gr bullets and shoot just as fast as a .300 or go to the .250gr(my favorite) and drop large bulls right now! In my humble opinion, the .338wm is more versatile than the .300wm, especially if you already have a .270 for lighter game.
guns762