Hopefully the French will be a straight swap for whatever rules I decide to use, although I may have problems with flank companies etc. But the British will definitely be a problem with their 16 figure units if they're painted up as distinct regiments.
My choice of rules is between Lasalle and FoG:N. I have both and I like elements of each of them so I think the final decision may come down to whether I have enough figures to make armies for the lists specified. I may have a problem with Lasalle as I don't think I'll have enough French troops to build an army with the listed requirements. Of course I can always try to trim things down but I'll only know for sure once the figures arrive. At least both systems use the same basing so that won't be a problem.
At the moment I'm leaning towards Lasalle as they seem to be a bit simpler to pick up, but I'll hunt around the net for some reviews and have a quick read through both again before I make my mind up.