I'm really surprised that the B7076 from Eccelfechen to Abington never made it to the short list. Although, it could be because the true joy of that road is only realised during a wet night ride.
For sheer character-building I don't think you can beat the A588 road to Cockerham. Google Maps
South America, and the Andes in particular, is full of hard-core, thrilling roads. One of my favourites is the mountain roller-coaster running from Cusco (the gateway to Machu Picchu) down towards the mysterious, fascinating Nazca Lines which are ancient geoglyphs of spiders, monkeys, hummingbirds and long lines scraped into the arid surface of the Nazca desert.