Bonjour Davout,
A very good question.. how fast did heavy cavalry charge?
My best reference would be "Imperial Bayonets" by George Nafziger...
pp. 201-202, Table 41[/i] shows that French Cavalry would Walk or Trot to within 230 paces of the target.. I suppose at the discretion of the Colonel... then Canter or Slow Gallop to within 80 paces... then Charge at Fast Gallop to contact... with the Charge speed being the fastest gallop possible without completely disordering the formation and losing frontal cohesion...
Cordialement, Duc d'Earl