As per LTLR and Angus, any "normal" cartridge would work fine. 25-06, 270 Win, 30-06 and 7mm Rem Mag come to mind. Factory ammo and brass (if you reload) is very readily available.
I'd look at an S2 Wby Vanguard and take it out and shoot it. If you want to move it up a notch then re-stock it as per recommendations in this thread:
Custom stock recommendations for older Vanguard
From what I've heard, though, the new S2 stock is much nicer than the previous plastic one.
My 270 Vanguard gets a new scope once this season is over. That should take it from a 250 yard rifle (regular duplex reticle now) to a 500 yard rifle for next season. I hope to do this as it is much easier to drag around the Vanguard than my Sendero.