Hello. You are obviously spending a lot of time worrying about ED before you've even chosen treatment.
I don't think my other half would have considered surgery for the same reason. As I said on an earlier post of yours, surgery wasn't really mentioned. But maybe had it been the best treatment for him he would have got on with it. He has a much higher sex drive than me even though he is 15 years older. So to him it was important when choosing treatment. He chose brachytherapy. Like you he was worried about ED after. I told him to worry about treatment first, then worry about ED after. I think stewing yourself up before you know how you are going to effected is silly. This is exactly what I said to him.
Brachy has effected things a little in that department, but not too bad. It says with radio treatment things in that department take years to show up, though I think a year on it has got better. Whereas prostate removal it is meant to get better with time.
Obviously I'm not answering your question but I'm just saying please don't spend too much time worrying about something that has not and may not happen. If you really feel that strongly then don't go for the treatment that has most chance of causing those side effects. But if it is the most recommended treatment then surely cure is best.
All the best.