Travelled Kidira - Kayes - Bamako about 6 weeks ago.
Kidira to Kayes is brand spanking new tarmac.
Kayes to Diema is perfect tarmac.
Diema to Didjeni used to be 120 miles of badly corrugated graded road but they are in the process of upgrading it at the moment - expect it to be about 10% complete by now. Up until the barrier at a village at the 70 mile point the piste to the left of the road is preferable. From the barrier on use the main road. None of it is particularly difficult though.
Didjeni to Bamako is perfect tarmac again. Don't know from Bamako to Kankan I'm afraid.