For Colorado elk? Assuming equal accuracy.
A) 308 caliber, 165 grain Partition at 2700 fps
B) 308 caliber, 180 grain Partition at 2650 fps or
C) 338 caliber, 210 grain Partition at 2400 fps
All of those would work. I'm assuming A would be 308w, B would be a 30-06, and C 338-06? Looks like fairly mild loads for all of them. I'd run the 30-06 with 180's, if that is indeed B in your list. However, if you can stand 30-06 loaded with 200gr partitions, that would be my absolute pick. That bullet just plows stuff in the grand ol 06...