I had a 6.5 Rem Mag in a m660 (20" Bl) back in 1970/71. While I used it mostly with 87gr. and 100gr. HP';s for groundhogs, a stiff load of 4831 and 140gr. Sierra's were also very accurate.
: Today, I'd use 120gr. XLC's, probably 4831SC and be very happy for all big game. The 120gr. XLC's will penetrate lenght-wise on British Columbian moose out to 300yds. at least.
: I would think the 22" bl. should get them moving up to 3,150fps to 3,200fps with top-end loads. Don't forget to start them .050" off the lands. RE-throating the chamber for .050" longer than the magazine body would be helpful for the "X"'s.
: Other than Barnes, I'd probably use 125gr. or 140gr. Partitions for everything.