Note: I have not personally set back a barrel.

However, the big thing that's going to matter is how torched the barrel is. With some of these hot 6mm and 6.5mm cartridges I've seen barrel cutaways where the first 12+ inches of the barrel were torched and fire cracked. In this case a set back may only get you a few hundred rounds of accurate life. So, in the sense of yobuck's post above it may not be worth it as you may only see 200-500rds out of it. a new barrel can had for about $300 and with the 260 (unless running very hot loads) will see at least 3000rds.

So the overall cost would be much more efficient by going with the brand new barrel over a set back. There are a few guys on the forum though that are more savy with barrel setbacks than I am, but I don't believe they were shooting matches with these barrels. So, your options are to take the chance and learn something/maybe see better results than what I've explained above or go with a new barrel that you will have full confidence with from the start.