CouesArcher
Neither of those guns is too much for mulies. I have taken a mule deer doe with my 300 win mag, never even thought twice about it. Something to keep in mind about the one you found though is that while having a muzzle brake will reduce felt recoil, the first time you fire it without earplugs will likely be the last. However, you can learn how to switch out barrels on the savages, set the headspacing, and presto, you have a new gun. Downside is having to rezero your scope after every change. At about $200 a barrel though, it's much easier to persuade your other half then buying a whole new rifle. No experience with the Howa so I won't comment either way.
As for the chamberings, everyone else said it true. Apples and Oranges. Chevy or Ford. Dem or Rep. With the same weight bullet, a 7mm will have a higher bc and therefore be flatter shooting. But with the 300 you have a higher end weight range of bullets to choose from. Do you want a little a round that shoots a hair flatter or a hits a smidge harder?
Another question to consider, is weather this will be a dedicated mulie gun, or will you use it for elk, bear antelope, coues, coyotes, etc.... That brings alot more into consideration.