When someone says Elk, I go to 7mm as the minimum. So a 7PRC would be a better choice over the 6.5PRC (for me). Or, the sleeper .280AI.
Yes, for all practical purposes, you have Elk covered to 400 yards no sweat. IMHO, you really should be looking at either a larger diameter, or longer range to separate from the .270 and 6.5s.
280AI is about 7mm Mag ballistics, based on the .30-06 case. Better case life, more efficient and easy to reload as opposed to the belteds. Now, what is better, a .280AI or a 7PRC. Well, on paper, the 7PRC wins. In practicality, the .280AI will be cheaper to load for. .280Rems actually shoot well out of them, to form the brass.
For Elk, again, IMHO, I want 7mm or better in caliber, 30 better, so maybe 300PRC, or bump up to another personal favorite, the .338-06. I love mine, and while I will take a 6.5 for my Cow Elk shortly, it is only since I recently had two discs replaced in my neck. Match rifle, comp and tripod...minimizing the recoil is paramount based on surgeon's orders.