270 is just fine for elk. 150 gr for sure, get the right bullet as its a large game animal not a deer. I.e. you want penetration and expansion. Not up anymore on what the best one is.
Get enough of those to sight the gun in and at least 20 for the hunt (take 40, you may need to re-sight if the gun gets knocked around).
If you can shoot it accurately, you are good to 300 yards.
The limitation is in the shooter not the cartridge. Know your limits and stay inside of them and you will do fine.