In reply to Trangia:
I'm not sure about the latter road (I've not heard of wupperthal).
The R364 from clanwilliam is good. Just anytime you turn off to a climbing area you get onto the sandy roads which are fine if you go slow. The only problem we had was driving to the fields of joy parking as the bushes were overgrown and we were worried about scratching the car on them (it was brand new).
Lots of roadworks just south of clanwilliam at the moment too, i think they're making a whole new road by the look of it, it's a huge job going on for many miles. Hopefully it will continue to see improvements!
I'll hopefully be back next year so the changes should be evident!