Your dad's numbers (Gleason of 6/7) look "good." If he has to have prostate cancer, those are the numbers to have.
One thing that hasn't been mentioned yet is finding a support group in your community. I facilitate a Man to Man Prostate Cancer Support Group which is co-sponsored by the American Cancer Society and USTOO, an international prostate cancer education and support group
(www.ustoo.org). I have men in my group who have had most of the treatments...surgery, including robotic assisted surgery, seed implants (radiation) and high dose radiation (temporary implants), proton treatment at Loma Linda, cryotherapy (freezing the prostate), watchful waiting and hormone therapy for a rising PSA after treatment (12 years ago). A distinct advantage of visiting a support group is the ability to converse with men who have been through different treatments. They have a perspective that "most" doctors don't have...they have "experience" with their treatment. My men are ready and willing to share, understanding that the information they give might help the newly diagnosed man determine which treatment he feels is best for him. And...your dad will probably have to decide on HIS OWN TREATMENT. My guess is that his urologist will explain what each treatment is like along with its possible side effects, but basically leave the final decision up to your dad. With all the different forms of treatment the men in my group had, they all went through some side effects, but all are still alive and enjoying life. I, personally (with my wife's input), chose surgery because I was comparatively young (64) and wanted to have radiation available as an option if surgery failed.
Sometimes one's other health problems, a high Gleason score or age eliminate certain forms of treatment from consideration. We are fortunate at this time to have so many treatment options available. There is no way I would tell your dad which treatment to have. Others, if they are truly being helpful, will simply share their personal experience with their treatment of choice and let your dad take it from there.
Oh, the other great thing about support groups: we actually see men who are surviving prostate cancer!