The most recent revision split the genus into 19 (!) species. Ten of the 19 can be seen on PCF:
https://www.planetcatfish.com/common/genus.php?genus_id=46#1800
Precisely my experience is too that many (most?) of the 19 species are nearly impossible to tell apart from external features.
Neither have I seen or heard of any e-cat bigger than 12"-18" in captivity and the only 3-footer I saw was in that Japanese Osaka Aquarium or some such video.
My only try with them was limited to a couple of years. It grew to 6"-8". Got sick on our NY to FL move. Perished some months later in 2011.