I've not got the .264, but almost; mines a .257wbymag.
I've found out why Wby still loads the 117gr RN in this cartridge. Out to ~300yds, it's a superb game killing bullet. It just dosen't know it's not supposed to shoot flat, so refuses to not do so. It's as flat shooting as you need and the bullet's terminal ballists are superlative, 3,000fps+ impact not withstanding, and considering it was designed for the .25-35 @ 2,200fps.......
BTW; it also performs exemplary from my .257Robt. at ~3,000fps over xx.xgr of IMR4831 (over listed max for non-+P Roberts loads; but is exactly max for the .25wssm).
So, I think that for elk, ect inside 300yds that the 154 and 160gr RN bullets will be absolute knock-outs. I believe IIRC that 10+ or so years ago, Finn Aagard wrote an article addressing such.
(My boat anchors have laminated wood, just like the paddles in my boats....)
I can't get much for velocity with H870, but RL25 and Retumbo give over 3,700fps with a 100gr and approach 3,400fps with a 115-120gr, so would be my starting attempts with a .264.