SBRT: Every day or every other day; proton or photon

Personally for radiation , I would choose low dose and more sessions.
I had IMRT 37 consecutive sessions (Mo - Fr) w/ short term ADT for persistent post-op PSA. All tx at Johns Hopkins.
And would do it again.
My total radiation dose was 66.6 gys; 1.8 gy per treatment session.
You are going to receive a similar total dose of radiation; just in different "strengths".
I didn't notice any benefit from 2 or 3 days w/o tx over weekends.
It is challenging to make decisions; treatment protocols are different with different ROs and are evolving. Proton was " hot" 3 yrs ago. IMRT has been updated. Different ideas on length and quantity of radiation and ADT therapy abound.
I chose a Center of Excellence and because I had confidence in my RO, I accepted his recommendations.
Best wishes.

Definitely a YES on getting the PROSTOX test. My understanding is that there are actually two of them. One for short term SBRT and another for the 20-40 session treatments. I did not do it, had the five proton over two weeks and had what I would say was a lot of urinary discomfort. Mostly over it now 4 months post treatment. But it would have been worthwhile to know how the test scored for me. It may have pushed me into the long format radiation.

I just finished 5 sessions of SBRT every other day for 10 days (MWFMW) at the Mayo in Rochester and was pleased with the result. I hesitate to try to paraphrase what my doctor told me about shorter timeframes. But it was something to the effect that prostate cancer responds better to higher doses over shorter periods. Perhaps someone can state that better or provide a better explanation.
Regardless though, the message I got from my doctor was that short course and long course radiation are equally effective. It might come down to what you want to do or the time you have. I had to drive an hour for each session so that definitely factored into my decision.
Didn't feel anything during the sessions. Started to get some symptoms the day it ended. A week after, feeling the need to pee more, but that is about it and to be expected and certainly not terrible.
The worse part for me was the anticipation of getting the SpaceOAR gel injected and I dreaded it for weeks. But that turned out to be nothing to worry about, they give you moderate sedation, and you won't remember or feel a thing (other than getting strapped into the stirrups).
I heard that exercising right before radiation makes it more effective as it oxygenates the tumor. I parked far away and ran for 15-20 minutes before each session. But you could also walk briskly or do the steps in the hospital too and probably get the same effect. I also adopted a FODMOP diet about a week before I started sessions. You don't want to be gassy or have things moving around down there. There was no need for pre-session enemas or anything for me.
Good luck.

@bjroc
I have asked my DR. at Mayo which machine they are going to use on me. They haven't answered my question yet. I'm guessing it w/b the Varian Probeam or the Hitachi.
The biggest question for me is would I want the advantage of the MRIdian with 2mm margins or the Proton CT guided with the stoppage of rays at the prostate target? Mayo doesn't have Mridian I'm told. Studies show markedly better results in complications with bladder, urethra issues with MRIdian.

@dribbles

If you have a location you can get to that has either proton like Probeam, or alternatively MRidian or MR Linac kind of machines you go to the one convenient to you. I mean I have a 6 hour drive for nearest of either, and will use Airbnb or something when I get set. So for me I am looking at just getting to any of those, we might as well go to the best we can get to reasonably and that may be how we make our choice. But given all the factors if one has both available, you would have to make a choice somehow. Mayo has Hope Lodge, which if I could ever get into Mayo proton I would try and stay there. I hope things are moving forward for you, keep in mind Mayo has all the best staff for calculating doses and all the rest of needed staff to make it the best too, so you are at a great place.