The A6 from Derby to Buxton is a nice road but it is chock-a-block with 30s, 40s, 50s, cameras and cars. You can have a nice ride when there are less people about but you are still stuffed with the limits.
There are much better routes - try the A515, A5012 and the B5023.
I live in Belper so I use part of this route regularly if Im going north into the Peak District. I usually get off it at Cromford and use the A5012 to get to Buxton as I think it is amore interesting and faster road. I will have to ride this whole route and check but Ive a feeling there are not many national speed limit areas nowadays - many sections are mostly 50mph and there are fair few 30mph zones. Its a nice scenic route if youve not done it before but I wouldn recommend it for a regular good blast. Avoid on bank holidays when its a car park.
A lovely road particularly after Chatsworth and towards Buxton. Road does say helicopter enforcement but I have been assured by a camera operator that this is not true - they don't have the equipment. However they do operate mobile units - see www.slowitdown.co.uk for locations before you ride.
Nice scenary that runs by the Ladybower reservoir, mostly good road surface. A thoroughly nice ride at differing speeds depending on your ability. Be aware that there is some police presence and this has probably increased since this road was mentioned in UK magazine RiDE as a favourite route.