I learned though true elk rounds start with .300 it's just that simple
Gosh, the good old 270 Winchester has filled many freezers with elk. If your dad is good with his existing rifle, it's not a bad choice.
Seems a little late in the game to be selecting a bullet weight if you're going to be launching in two days. Do you have the 7mm Rem mag sighted-in with one of your bullet choices now?
Between the two, I'd tend towards the 160 gr Nosler Partition. That bullet is well proven from the various 7mm magnums. I have used a different Berger VLD with good success on mule deer. Just thinking the Partition might be a better choice if your dad gets a bad angle on the shot and more penetration is required.
Enjoy the hunt! Pretty cool that you're hunting with your dad. I like that.
Best of luck to you both, whichever rifles & bullets you choose.
Guy
Was gonna go with the VLD but the Partition has performed flawlessly for years for me.