Lots of members on the forum have them, they are also called Tigrinus catfish, Zebra Shovelnose, Merodontotus Tigrinus (sp?)
Around 30" with some getting larger. Flow depends on the size of the tank greatly. 5500GPH in a 600 gallon might be a bit excessive. I would really say it depends on the dimensions of your 600 and the way you have the return lines routed to the tank. That would probably be fine if you have 2-4 returns into the tank spreading the current out a bit ~Trent