Hmmmm
My two out of three of my favorite calibers 270 & 300.
(Not necessarily cartridges, but calibers).
Guess it'd depend on the bullets used, & also a good deal on personal preference. They're pretty close, but, when comparing cartridges with very similar ballistic numbers, I always give the nodd to the larger caliber where Elk size critters are concerned. Just my opinion, & this philosophy has served me well.
Not at all dissin on the 270. It's PLENTY CAPABLE of dumping an Elk at LR with the right bullet. Like I said its one of my three favorite calibers of all time. 270, 300, & 338. Just doesn't get any better.
FYI if you wanna run JBM or something like it, with Simmilar BC hunting bullets, at simmilar realistic velocity, try comparing a .277 cal 140 Accubond with a .496 BC at 3100+' fps (270Roy) to a .308 cal 180 Accubond at 3100' fps with a .505 BC (300WSM)
Ya I realize these aren't the "heavies" but they're common for caliber & very very Simmilar for flight, etc & commonly used for deer/elk size game at ranges from 0-650 +/-
If you want a bit more range, & are willing to compare dedicated Long Range Only rigs, Throw the Matrix or Berger bullets in the mix & you just tipped over the cookie jar! It's anybody's guess on any given day depending on barrel length, twist rate, case capacity, SD, BC, etc. my initial guess would be the 270Roy would edge out the 300WSM due to case capacity alone. The 300WSM just doesn't have the capacity vs bore diameter ratio, to shove the heavy, super BC bullets at a competitive enough speed to take advantage of them.
Given that my style of hunting is 0-650 ish, & I shoot 140AB's at 3100 from my 270WSM, & 180AB's at 3100 from my 300WSM I have my "deer gun, & my elk gun" for my average hunting scenario that I'd typically encounter.
If I wanted to go "Long" I'd use a big 338, but that's just me.