I am going to sound like the Grim Reaper but your PSA went up so high post-op that it is hard to believe it is just a few stray cells that can be mopped up with some RT.
I think the surgeon is being over-optimistic but I wasn't at the appointment with you ... what did he say about the PSA being so high? Did he acknowledge that cure was unlikely or was he suggesting that it was still a realistic aim? More to the point, what chance did the onco give you a couple of weeks ago? He is the expert in this stuff, not the uro.
On the other hand, you presumably don't have to decide yet? Or you could say yes now and then dip out later? What do you have to lose? John's salvage RT seems to have failed but he doesn't regret having it because he had no problems and it has given him a 5 year respite.
Generally speaking, a low post-op PSA that climbs slowly is indicative of left overs in the prostate bed while a high post-op PSA and/or rapid climb are suggestive of mets. Did either specialist discuss patterns with you?