Hello - I am surprised that with a 4.1 ng/ml PSA, that you are at a 4+3=7 Gleason score with 13 out of 15 cores positive (that is a LOT of cores...it is usually a 12 core biopsy at most). Suggestions:
1) If your urologist did not order the test, MAKE SURE they order the "Decipher Test". It is a test that screens for 22 prostate-cancer-specific genes and mutations that help determine short and long term rate and risk of progression/reoccurence, as well as your predicted longevity.
2) With what is already a 4+3=7 Gleason score (not the slightly more preferable 3+4=7), I'd go straight for DaVinci Robotic-Assisted Radical Prostatectomy. "Why wait?" Like my doctor told me even being a 3+4=7, and after I asked what my options were including "Active Surveillance", he said: "You're already at a moderate risk level, why would you want to do Active Surveillance?...the cancer is there, it is only going to continue to grow and spread..it is NOT going to go away." Then without a pause he said: "I'm taking your prostate." I'm glad he did because my pathology was much worse than what the 3+4=7 Gleason score might have suggested (my PSA was slightly higher at 6.1 ng/ml). My urologist changed his overly confident mindset of "you'll be alive in 15 years", to one of my "cancer is an aggressive one...we need to talk about radiation (after the RP)."
3) The PET Scan is quick and easy - 30 minutes of slow incremental scanning of your body from neck down to mid-thigh looking for any Gallium 68 uptake that may be elsewhere in your body. What you want is that all the uptake was/is confined to the prostate, showing that the cancer has not spread to other areas (metastasis). I was lucky, my was all confined to the prostate, but that is all the PET Scan tells you. It tells you nothing of pathology.
4) Make sure that your urologist has done a couple thousand DaVinci RP's, and that you are having it done at a highly regarded hospital, preferably a teaching institution like a university medical center (U of A)...NOT your local community hospital. Actually, most local community hospitals can't cost-justify having a DaVinci Robotic system...you will only find them in 300-400 "+" bed hospitals that see a LOT of patients. BTW...the DaVinci method is preferred by most urologists because it is a single, 2.5" incision about 3 inches below your navel, instead of "five" 3/4" incisions all around your lower abdomen with the traditional/older method. You just want "best practices", "best technology", and "best urologist" in your region.
The main takeaway is that a Gleason Score is only the tip of the iceberg that tells you have prostate cancer and to what "preliminary" extent. If there is one thing I have learned through my own case and reading many other accounts here - like yours - is that the Gleason Score and a PSA that is only 4.1 ng/ml can fool you into thinking your cancer is not aggressive or aggressive "yet", when in fact, it could already be quite aggressive.
Good luck with everything.