Just a completed a leisurely version of this - starting in Abergavveny and finishing in Bangor. I kept the daily distances pretty modest and my lack of fitness, the gradient and what Sustrans think passes for a touring-suitable bike path meant I wouldn't have wanted to do much more. Also managed to miss out the steepest bit coming out of Corris, which, for the reasons above, I was not sorry about and lapped up the short sojourn into smooth tarmac instead.
Some really beautiful bits - which my photos don't do justice. And this being July in the U.K., quite a lot of rain and headwinds. Was not sorry not to be camping.