Hi, Ed--
There's no pat answer to what the PSA level to trigger SRT for you should be. Waiting for one more data point in 3 months, to give a better sense of PSA-DT, seems reasonable. I think if I were you, though, I'd want to hook up now with a good RO, both to get a second opinion and for the comfort of knowing who you'll be working with if/when you need to do SRT. I'd also want to get views on whether ADT should be added.
G8 is nothing to trifle with, but your 7 years before any hint of BCR is a favorable sign. For a recent review of the literature on BCR after RP, see
Biochemical recurrence after radical prostatectomy: what does it mean?Keep us posted, and keep your chin up!