multimap.com gives it at 583 km and almost 6 hours. I drove to Monaco from right up here (Flumserberg) and did it in less than 5 hours, but that was very early morning.
Wow ...which route did you take?
6.5 hours is about right from Geneva if you keep to the limits and take a rest break. I did it to Nice in just over 6 hours via the Great St. Bernard Tunnel which is closer to where I live at the other end of the lake. I used ViaMichelin route planner which said 5hrs 30 minutes. I had a 20 min. break and no hold ups.