Shooting elk in timber will usually mean tracking, no matter the cartridge. Blood alone can't be relied on as a tracking guide no matter what it's been shot with, so you've got to be able to read more than that. I've had bulls go equally far shot with the 338 WM, 300 WSM, 30-06, 270, 308 or 7-08. I've had them drop in their tracks with the 308 and 30-06 without CNS hits.
I will agree that it's not unwise to shoot the largest rifle you're comfortable with, on the other hand, it conserves more energy packing a light rifle rather than a heavy one all day in the mountains. For me, the "ultimate" elk rifle would be a 22" bbl'd 338 WM weighing around 7.5 scoped, with sling and rounds. Problem is, I don't want to pack or shoot a 7.5lb 338 WM anymore, so pack a 6.5lb 308 win!
Funny how elk just die when you shoot them right with a good bullet. Bullet placement and bullet quality trump cartridge size.
