Just returned from a tour of France and took the N151 south out of Auxerre. A good road - well surfaced, quiet and lots of sweeping bends mixed fast straights. Gradients not severe but enough to make it interesting. This is the sort of road which makes it so much fun to avoid the motorways in France.
Take the D977 from Nevers to Varzy, then the N151 between Varzy and Auxerre.
A fast sweeping road, scenery not spectacular but a road you can cover ground quickly without getting bored.
Watch for a couple of speed cameras, one at either end of this route.