Wales is brilliant
the north has tourists and way too many speed cameras but the south and centre!! :-D :-D :-D
Almost any 3 figure A road (e.g A111 or A222) will give you 100->30->110->20 cross country riding with loads of complex turns. I won't suggest any realnumbers as apparently local police have been surfing the web to see where to put their 'orrible cameras.
I just turn down any interesting road & then do it again, keep doing the same using the sun as a compass (or if no sun the direction of the rain after all it is wales) until I have 25mile of petrol left then find a town & repeat.
On the busier straighter roads be a bit careful of the boy-racers on full on 2006 sports bikes. You can reckognise them as they have to overtake you across whitelines & with zero visibility to prove their manhood! I understand the welsh name for them is Knobbheddds.
Have a brilliant time! Jon