Janne's point is a good one. I find in my own collection, with "classic" figures, that I can mix them with not too much effort. An Imrie-Risley French hussar c 1790 with a mirliton makes a pretty good Prussian SYW hussar, next to a Stadden Prussian cuirassier, for example. The hussars were recruited from men of smaller stature, generally, and Stadden captured the robust stature of the cuirassiers. And both are reasonably proportioned. I look for those kind of things, when I'm looking for figures to add to the collection.
Brad