Jim -
I recently went through a similar experience with my Savage sporter-weight .22-250. After looking at rebarrel costs, I sold it, threw in $150 and got a used like-new Ruger M77 in .257 Roberts, with a Leupold in the rings.
With a Parker-Hale, though, I would definitely go a different route. Re-chambering to AI is inexpensive, and if it fixes the problem, great. If it doesn't fix the problem, a rebarrel would be in order.
The 6.5 is getting close to the 7mm, especially since this has been a varmint gun. I'd probably stick with the .243 (assuming you have dies and brass). If I decided to step up a notch, I'd probably go to the .257 Roberts or Roberts AI. After that it would be a toss-up -- 6.5mmx55, 260 Rem or .308.
Good luck, let us know what you do.