If you're getting .5moa accuracy at 560 yards from your current rifle now and you like the cartridge for which it is chambered (257wby), why rebarrel?
If you're not a "junkie" per se, how about 'accurizing' your rifle. Which is to say, do a few things to maximize the rifle as is. This would include...
1. New stock (HS precision is a good choice)
2. Have your action bedded in the new stock
3. tune your factory trigger to 2.5lbs or lighter. Better yet, replace the factory trigger with a Timney or Jewel trigger.
5. Lap your bolt's locking lugs. This will ensure complete contact/lock up.
6. Recrown your barrel. Often the crown on factory barrels is not completely perpendicular to the bore of the rifle. Recrowning will correct this.
As an example, here's my nephew's rifle that has had this work done....
Nephew's Transformed Rifle!
With the exception of recrowning the barrel, all of the steps above, will 'stay' with the rifle even if you rebarrel. Accurizing can be done for ~$225
If you're set on rebarreling, there are many good barrel manufacturers...krieger (fine for hunting), brux, shilen, hart just to name a few.
As to cartridge chambering, length and contour, that would depend on your intended use. If the rifle will be a 'prone' gun where you will take it to a firing point, then shoot, you can go with a heavier contour (generally more accurate) because you will not be carrying the rifle much.
if your intended use is for it to be more of an 'all around' then you might look at a more 'standard' contour (similar to your current contour or even a bit lighter).
In terms of getting a barrel quickly, check out www.bugholes.com
They are an LRH sponsor and have many barrels on-hand and ready to ship.