Dave, I was in a similar situation, similar age to yourself. My PSA was 20, with a Gleeson Score of 3+4. I was offered RP to remove it in February, however because I knew it was slow growing, I knew I did not have to rush into it. Particularly as I knew the side effects and effects on quality of life. I explored the HIFU option, even went for another Biopsy, but my pca was multifocal, I had a combination of Gleeson 3+4 and 3+3, so what would have happened was I HIFU would have been used on the right side and they would have left the 3+3 on AS. I thought long and hard and decided to go with the RP. Probably the best thing in my case, as my prostate size was the largest they have seen!
I would advice you to consider all your options and not rush into any of the invasive treatment options, that is what I did and even though I am going through the effects of the surgery (10weeks on) with ED and mild incontinence, I think I am fairly comfortable with my decision. I remember getting the call after my biopsy with the Nurse telling me I had PCa, I remember begging her to put me on AS, she declined saying Gleeson Score 3+3 was the maximum!