There may be merit in the Elk at 500yd concern with either of these rounds. I've not hunted elk at any distance, much less 500yds, but they're big, tenacious creatures from what I hear, and I'd rather have more reach. Options abound, including the WSM's as have already been mentioned, and also the 7mmRemMag, 300WinMag, 300Wby, all of which are available in the rifle you have selected. If you handload, you could make any of these rounds in the magnum class shoot like the 30-06, but if you're limited to factory ammo, I'd go with the 7mmRemMag, as it has the ability to launch 175gr bullets at roughly 2850 out of the 24" barrel of the Vanguard, which ought to be enough to reach out across 500yds and touch an elk just right. Energy at that distance would be on the order of just above 1500lbs, which I have on good authority is plenty for elk. You could even go to something like a 160gr bullet of heavy construction and have even slightly more velocity and energy, which would only enhance your prospects. The nice thing about the 7mmRemMag is that it is an easy round to shoot with only slightly more recoil than the 30-06, if more at all. It is a very manageable round with plenty of reach and potential. Factory ammo is going to be a tad more than the 30-06/270Win, though not a ton more, and in line with or below the price of everything else mentioned.
Really, if you think you're going to shoot past about 350yds, more depends on the shooter than the rifle when you're talking about the rounds mentioned here. Practice a ton, and you'll be fine no matter what you choose. And with regard to your original question, the Sub-MOA Vanguard is one fine rifle, for sure.