It is ok to set the shoulder back 0ne thread and clean up the chamber, But if more needs to be taken off you should start over with a new tenon and threads. It is very hard to pick up threads
and do them correct, so I don't recommend doing it.
As to the original posters question about 6.5s, I like them but like so many calibers they have there limits and IMO the 6.5 STW would exceed those limits with no gain.
I built a long barrel 7mm STW (31") and it would exceed the 140 grain bullets limit of over 3700
ft/sec (I reached 3800 ft/sec but the bullets lost there jackets and accuracy fell way off) and the barrel left me with just under 300 rounds down the tube.
The 6.5s that I have had good luck with are the 6.5x47, 6.5 284, 260 Remington and the 264 win mag(which is about the limit of decent barrel life) I am sure there are more 6.5s that perform well
and have good barrel life, good case life and are very accurate.
If you like the STWs go with the 7mm. If you want a 6.5 there are plenty to chose from that will
make you happy.
Just an opinion
J E CUSTOM