It's an easy drive - certainly the way we use, which is to take the D820/D890 south of Brive La Gaillarde, then across to Martel, by-passing Rocamadour, and down to Figeac, Rodez, then the N88 via Flavin, Pont de Salars, and then to wherever you're staying on the lake. We prefer that way down to the Mediterranean as we store our caravan near Chateauroux, so use the free A20, then cross-country to the also free A75 and south.