Madkoifish, I've been a HUGE fan of your work, even since I first saw them, and has been a large inspiration for me to one day get into 3D modeling one of these days, and to post my sketches and drawings in the meantime. It is a huge shame that it appears that a large portion of your past work seems to have disappeared, because everything that you do is fantastic. Not only your modeling skills, but also your attention to detail, is truly remarkable.
So you can imagine my surprise and excitement when I saw your username as the poster for this thread.
Once again, all of your work is fantastic, and every image and render eye candy.
I've had a bit of a conversation with myself however, and have decided that Acheron and Phlegethon DEFINITELY do not look like they belong to the Potamos class like the Lethe. Yes, they share the same components, but then, so do the Longbow, Constitution, and Decatur, but make them the same class, that most certainly does not, and they have a more similar configuration than the Lethe, Acheron, and Phlegethon (the latter of which looks more like a Surya or Miranda class Frigate-albeit that the nacelles are above instead).
You can come up with the class names if you want, or just assume that the Acheron and Phlegethon are one-offs. For now, that is what I've pretty much have done.
Anyways, I look forward to seeing more of your work here, and as a fellow artist and designer, I welcome you heartily to TrekBBS!