I am aware I'm responding late to this subject, but I've found the Cat and Fiddle in Derbyshire to be an excellent road, on account of having driven it four times. Twice, in beautiful sunny conditions, and twice, when it was snowing.
In the sunny conditions, I found it to be a most enjoyable road on account of being able to overtake very easily, due to a lot of really clear cross views across bends etc. Great fun, and I had no need to worry about exceeding a 50 mph average. I suspect I'd managed to average 25, possibly 30 mph, but certainly no more. It was a nice road on which to practice limit point judgement and trying to use acceleration sense to round the bends with no braking necessary. Good fun.
The second round trip, I passed over it on December 10th, which is the day the snow fell. On the first passing, it was probably 1pm, so mostly well gritted and clear of snow, so no real problems. Still took it easy and made sure to brake gently and included plenty of allowances for possible misjudgements. On the way back, however, it was 7pm, and it had been snowing solidly all afternoon. The result - a road which was completely covered in a mixture of slush and fresh snow. Probably the most entertaining and fun drive I've ever had, driving along in pitch black in my tiny FWD eco hatch on summer tyres (which are the eco-low-friction type), and overtaking massive 4x4s struggling to go anywhere useful. I've never enjoyed a drive as much as that. At one point the snow was so heavy I could not see much more than 15 or 20 metres. It was great fun, and I would love the opportunity to do it again, but perhaps in the day time so I could see where was safest to slither about a bit more