There is a structure to the fines: Up to 30kmh over the limit, slap on the wrists and fine of about 150 euros. 30-55 kmh over the limit, bigger fine and possible ban; more than 55kmh over the limit, 750 euro fine, confiscation of licence and a ban. Game over.
The answer? Swap the Porsche for an old MG.
Still much easier to speed in France than the UK, despite the clampdown. And if you steer clear of the popular routes to Le Mans, you don't see les rozzeurs.