Hi art and sorry to welcome you to the club.
If you haven't already, you may benefit from reading the sticky:
Newly diagnosed with PC? – read this thread first I think Mayo may have a dedicated prostate pathologist who reads biopsy slides - I seem to remember that Bostwick started there. If not, a second opinion on them from Bostwick or Epstein may be a good idea. It's possible to get misreads from even a saturation biopsy if the pathologist wasn't dedicated to reading only prostate biopsies.
I agree with JNF that you may want to understand why your PSA is so high for a GS 6. You may have a very large prostate, prostatitis, or urinary retention going on at the same time. A large prostate and urinary retention may preclude LDR brachy treatment.
In addition to SBRT and surgery, either kind of brachytherapy (as monotherapies) may be good options for you as well. I think conventional IMRT as primary therapy is outmoded, and there isn't any proven benefit to protons that justifies its cost.
I had SBRT - CyberKnife is one brand name for the linear accelerator system used doing SBRT treatments. I was treated with a different machine, but they are pretty much equivalent in the hands of an experienced radiation oncologist. See links in my signature.
As you've just learned, you have to talk to experts in each particular treatment specialty, and you can't rely very much on what others say who are not experienced in that specialty.
While surgery is not a good option if radiation fails, there are several other salvage options, including salvage brachytherapy, SBRT or cryotherapy. Local failures are rare after any treatment, surgery or radiation, for a GS 6, so that ought not drive your decision.