If you take a look at page 127 there is a list of basic stats for the various troop types. Using that as a basis you might then add the Elite useful rule on page 85, although Elite Light Cavalry are already listed.
However, if I understand it correctly, does it not mean that Chasseurs of the Guard are inferior to ordinary line dragons, and not even equal to the poorer catagory of Russian dragoon who presumably would not qualify for the Heavy cavalry bonus?
Yes, but you can look at the Useful Rules section and maybe add something from there to beef them up a little, like giving them Elite, which would give them the ability to overcome disorder (page 89). You can further modify it by altering the dice roll required accordingly. There are other additions you could put in there as you feel appropriate.
I wouldn't get too caught up in trying to match the stats. of a unit to its title. The 1st KGL Hussars at Waterloo had on average bigger horses than the Royal North British Dragoons, and British cavalry didn't fight in different formations depending on their title. I think you have to base it on how the actual unit performed. Bowden put forward the interesting idea of distinguishing 'battle' cavalry and '2nd rate' cavalry for Napoleonic games. I'd see the 1st KGL in the former category, while the Dutch-Belgian 'Heavies' were certainly in the second. One of the great things about BP (and HC) is the ability to add on a special rule here and there to those special formations. Equally simple to change the main stat line.
I think you will find that most lance armed cavalry only had lance for the front rank.
I was not aware that Russian hussars dropped the lance after 1812, although to be honest there are so little references to it being used, I do wonder if it was one of those items of equipment that was quietly dropped as soon as they left the depot.
However, if it was used it might explain how the Russian hussars maintained such a consistently high standard of combat performance, althogh the quality of their manpower was btter than the norm.