Hey Pathfinder. Those aren't bad at all, still they are a bit different from the actual ships. Here is a link to a B5 RPG which currently is using these ships:
http://www.sgnOnline.com/vb/showthre...=&threadid=789
Those are small pics of the high poly models. If you need multi-angle shots, I can provide them for you using the models I have for my ST Armada 2 B5TC. I can send you pictures of that and any other ship you need to give you an idea what they look like. Just let me know how it'd be best for you; if by E-mail or if you have MSN Meesenger I can give them to you directly.
As for the sizes, the Tethys is a Cutter (that's the classification of patrol boats used by the Coast Guard) so I suppose the nearest thing in SE4 could be either Escort or Scout. The Sagittaius is a Guided Missile Cruiser so you can classify it as any kind of Cruiser you want, though the Sagittarius is used as a ranged artillery ship only, no pulse or beam cannons so maybe it might be considered less than the Hyperion which has both pulse and beams (maybe the Sag can be a light cruiser? Or any class that might be used as a artillery ship). The Artemis is a Heavy Frigate. Frigates usually have special roles and weapons suited for that role. The Artemis is equipped with 4 forward and 2 backward Rail Guns. Rail Guns (in case you don't know) are cannons that use series of magnets to propel uranium shells at extremely high velocities, these shells punch through enemy armor and explode releasing high radiation (kinda double wammy) the trouble with Rail Guns is that they have to be constantly reloaded since they use munitions, still the Artemis is a bit bigger than the Olympus Corvette (somewhere between 450-500 meters in length-Olympus is 444m) and the Artemis is also made with the thickest armor for its size making it a really deadly opponent (it's listed as the only ship really capable of damaging Minbari Sharlins dring the war).