150gr NP will work fine for your elk hunt. My hunting partner uses speer 160 gr Grand Slams in his 280 rem which work very well on elk, moose or deer. Nitrex ammo use to load this for the 280 and it was reasonable to boot. You may try locating some of the 160 gr grandslams by Nitrex. The TBBC loaded by Federal would be another solid choice. Personally I think the 140 gr Failsafes should also get the job done. I have used them on both moose and elk in a 270 win with good results, I just limited my shots to ensure higher % outcomes.