A factory 6.5 x 284 may be the ticket; likewise the 260 Remy (or a variant).

If that's not enough soup for him (and it is for an elk), check out splattermatic's post on the 7mm Mag.

Long range is a lot about practice and practice is a lot about recoil. 'Course, if your pal is willing to lug a 10 lb rifle, more options await.

I do not entertain hypotheticals. The world itself is vexing enough. -- Col. Stonehill