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