just my 2 cents, I would keep the 300wsm barrel, u know as soon as u change or get rid of it you'll need it for a hunting trip. (besides it sounds like it shoots well,) Since u have a Savage and u mentioned switch-barrel, I honestly would say get a Pre-Fit Barrel from Sharp Shooter Supply in say 6br 1-8(heavy bullets) or 1-10twist(lighter varmint bullets) u mentioned ranges in 300-600yd, and this caliber covers that and proves to be very accurate to those ranges. And u can get a replacement bolt face Sharp Shooter Supply - The Savage Specialists
I think in the end, ur goona spend a tad more, however you'll have 2 calibers to choose from!!
Next step u wanted is to watch bullet impact, go heavy with the barrel and would suggest a brake from 308nate.
Another suggestion for watching bullet impact would say, look at some of the 20 caliber wilcats out there. I'm shooting the 20 TAC and I can watch the mini's I shoot at 400yd explode off the board. There are some real hot-rod 20's out there that can really perform well out to 600+ and the gun will move with little retort.
hope this helps