RE: Best 7mm Rem Mag cartridge for Elk??????
Start with the 160 parts. Another federal ammo to try would be the 160 Accubonds. I really like the failsafes as well. Like mentioned shoot the bullet your gun likes the best and as long as it is designed for the larger game like Elk you'll be just fine.
I don't favor remmington ammo, so can't comment on the ultra in the 7 rem mag. I did see a poor result in an 06 with 150 gr version last fall on wt buck that lends me to believe better choices are available in ammo.