Two more cents for consideration:
My current elk rifle is a .300 RUM. Still, a retired USFWS warden friend of mine used a .270 and .280 to cull untold scores of elk during his career, and almost always with a single shot. This was in the days before the modern super/premium bullet. Admittedly, he carries a .300 WSM nowadays.
I'll ask him for more details later, such as range, bullet type, etc., but in any case, his extensive experience (far beyond what I'd have in multiple lifetimes) surely demonstrates the effectiveness of the '06 and its progeny on elk.
On the other end of the popular elk cartridge spectrum, I've seen a buddy of mine deliver multiple hits from his .340 Wby to bring down a couple nice bulls (he shoots the pre-TSX XBT). Admittedly, his initial shots were raking shots.
On the first, the bull showed no signs of stopping after being hit twice (even though we found later that both reached the boiler room), and we eventually found him bedded, mortally wounded but still alert. On the other bull, it dropped within 100 yards of the initial hit, and upon post-mortem inspection, either hit should have done the trick solo. It just wasn't DRT performance.
This isn't a criticism of the .340 WBY or the Barnes X. Rather, this is yet another illustration of how ideal shot placement with a more standard cartridge can be more immediately effective than a super magnum and less than ideal shot angle/placement. This also shows how a powerful chambering paired with a super-premium bullet can have performance advantages if you're one to take a raking shot, given nothing else.
Sitting here at my PC, it's easy to say I'd pass up a less than ideal shot...but after eager anticipation, costly travel and enduring the better part of a week in a frozen elk camp at 8500', many an ethical compass may be tempted to sway a little should "Mr. 400" present only a Texas heart-shot pose at an intermediate range such as 250 yards.
That's where IMHO (very humble), unless necessitated by economics or ability, I generally do not recommend using marginal or light for quarry loads (by chambering and/or projectile). Your '06 is surely not light for elk.
