I road with a Honda CB1100 in March 2016: It was a nice road (but I have seen better in this Eastern Europe). Nonetheless, on the way to Sofia you should give it a try
Very beautiful short route. It goes around the beautiful Pchelina lake between Kovachevtsi and Lobosh.
The surface is very good and there are lots of nice corners.
There's pretty much no traffic.
There is dust on the road in the spring, but should be fine later during the year.