Re: 7x64 v 280 Rem.
i have a 7x64 in a mauser model 66 that i brought back from germany with me some years ago.
i also have a 280ai, and between the 2, i'd go regular 280, as brass and if needed, factory ammo is readily available.
7x64 is pretty pricey, if i remember correctly. i do have a stash, if i ever want to pull the old girl out of the safe and load some up for her.
ballistically, they are darn near identical in performance. i load 55.5 grains of imr4350 under a 139 btsp, for around 3,000 fps, in the 7x64. now remember this is in my gun and is safe in my gun. if you have a 7x64 start lower and work up please.
go 280 and don't look back...