The Sako would be an excellent choice and a step up from a M700, without a doubt. As far as a chambering, the .270WBY is a hot number but very $$ for ammo, very! If you're gonna reload, then that's not a serious matter, but if you're going to shoot factory loads, the WSM version is a lot easier on the old wallet.
I would not handicap my choice by not wanting to shoot it often, because ammo was so pricey. The .270 WSM is a step up from the standard .270 Win and a very flat shooting cartridge. The one I shoot, on a Model Seven action has moderate recoil, on a par with an '06 shooting 180gr to my shoulder.
Lots of options out there for buying ammo and lots more choices for the WSM version.