I'm sorry, but that latest one you have looks to me like some form of destroyer.
How? Easy, fit on large guns on the tops and bottoms of those wings, similar to the guns on homeworld's heavy cruiser, also give the bottom section a single "stick" poping out similar to the bottom forward array on the Orion. (i.e. have such an array portrude from the bottom)
Then on the underside at the rear, have a single engine array which comes out similar to the Deimoses' (i.e. a small "box" with the engines within it replaces the round thrusters you have)
I'd make it a little larger than a Deimos, and smaller than an Orion, say 1.2-1.6km?
I hope you could do up a version based on this idea.

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AceStaff member FreeSpace Watch
http://freespace.volitionwatch.com/