Glad I got the trip in in the 911 this summer then
As for whether you'd trip an average 60 on the way round that very much depends how the cameras are spaced out as it won't be just one at the beginning and end of each stretch.
The side from Pentrefoelas Northwards in a clockwise direction would probably be ok as its reasonably twisty. You'd not be so lucky south past Llyn Brenig, however, I'd expect.
PDK frees up your left hand so you can scratch your vagina.