Sorry not got a any Confederettes, but have a lot of Napoleonettes. Here's what I have found matches them. Napoleonettes are 12/13mm to the eye, so I too have oft wondered if big 10mm would tie in.
Naismith are spot on, identical. Recently changed hands, there was an ACW range but not in production for a long time. Now listed on the website but no products in the range yet. Might be worth an e-mail? (Now NaismithRoundway)
Minifigs: cavalry matches in but current infantry are considerably taller. Wagons and limbers match in reasonably well, artillery is noticeably bigger though. Vintage ranges match better.
Peter Pig: they don't make Napoleonics bar a couple of packs, but comparing my PP ECW to Napoleonettes they are a very good match. Some of the newer sculpts are marginally taller but not by very much. Big ACW range, might be worth a sample pack to see.
Essex: whole head and shako taller.
Hallmark, slender (in comparison) and a bit taller. Noticeably different. Sculpting style too different.
Roundway, much taller, very different stylewise. Not a good mix.
I've not tried them but Warrior are supposed to match quite well. Know nothing about them, don't even know if they make an ACW range.