I promise I will get to the meat of the question in a moment, but I'd like to start with your premise. The minimum height for a Napoleonic French cuirassier was five feet eight inches. As this was already significantly above the average height, we can probably assume that most cuirassiers would have been close to that height and weighed, oh, 150 pounds or so. The average heavy cavalry horse was a strong but by no means enormous horse of fifteen hands and two inches, probably weighing in the area of 1100-1200 pounds. Even if we allow a generous hundred pounds for the rider's armor and weapons, personal effects, and saddle, that leaves us quite a bit short of a ton.

That's not so far off from an early 14th century French man-at-arms. Medieval western European warriors averaged about 5'9", so we're dealing with a very similarly sized individual. The armor would be slightly heavier - 45 to 65 pounds - and if he was a rich soldier, he might ride a slightly heavier horse into battle, but it would still be far smaller than the draft horses employed by modern jousting enthusiasts. Mounted and armed, I can't see him weighing more than perhaps 1600 pounds.