Thanks for all the suggestions, though I fear that even 6cm likely isn't going to cut it, they need to be 65mm at least to work. There are other prepaints in the 60mm range, like First Legion and Kronprinz, but even those are too small IMO.
I have that musketeer from your second link and it's much too small IMO. It's not just height, but overall bulk of the figures as well, his face is just tiny compared to the K&C stuff. I have given up hope on 54mm being close enough. Closest I have found is the H.M. Beneito range and even that isn't quite right.