I like the first Black Swan Knight helmet. The second and third helmets are okay, but the last three look like feather dusters, not very exciting. Will their heads be swappable with the Dragon Knights' and Albus Custodes'?
The armor itself looks like it will match the infantry elves pretty well. It looks stylish, although I wouldn't mind if you added a bit more flair. I'll have to see the 3D renders to judge the horse and weapons. All in all, they look like they will be a solid unit of cavalry that will mix well with your previous elves.