I did the stretch north from Clermont l'Herault to Millau. It's brilliant. At one stage I could see cars very high on the mountain then was amazed when I realised it was the same road. Once on that high ground it becomes relatively normal, but that's the price to pay to cross the Viaduc de Millau, which I found breathtaking.
Its an autoroute, so according to the form book it should have nothing of interest to offer bikers beyond being an efficient way to get to and from the Pyrenees. However, this one bucks the trend - its a twisty and interesting Motorway that passes through reasonably stunning scenery! I rated it a 5 for spectacular scenery mainly for the Millau viaduct at the south end, which is possibly one of the engineering wonders of the modern world, but the setting on the way down aren too shabby either. Somebody above said this was a motorcyclists motorway, and it definitely is. However, watch for les flics, who police this road heavily, and try not to catch their eye. France seems a lot less laid back about... err... making good progress... than it used to be...
We did the N75 south from Clermont Ferand to Millau. First section relatively uninteresting but this motorway just gets better the further south you go. Put out of your mind any preconceptions about motorways UK style - this is fast, well surfaced, light with traffic, climbing, diving and long sweeping bends. However, a word of warning, it is policed and we were caught by well concealed Gendarmerie car on a slip road with a speed gun, just before we got to Millau. Fortunately we were only doing 100 mph and got away with one of us getting a 90 euro fine. A fantastic road but you have been warned!!
The A75 is (if there is such a thing), a motorcyclists motorway. Corner after corner of high speed open dual carriageway on very good quality motorway style surface. This section also offers easy access to the Gorges du Tarn and Viaduc du Garabit. The marked end point for this route is just before the peage section, but if you continue after that, it takes you over the spectacular and massive new Viaduc du Millau. Ridden at Dusk on a Saturday in June was excellent, no traffic to speak of