It looks like a MK2 Intrepid.
Heh, the very first thought I had after seeing the first image: "Oooh look, an Intrepid variant/refit"
![:P](http://bc-central.net/forums/Smileys/BCSmileys/tongue2.gif)
EDIT: After reviewing all posted images thus far, my only suggestion (if not too difficult), would be to lengthen the nacelles somewhat (10-15%), backwards. Forward end of the nacelles should remain as is, but extend them closer to the back end of the shuttlebay area. I realize you have begun mapping/texturing the ship, so this might not be possible at this juncture.
Still thou, I like what i'm seeing so far. Being that it's got some influence from Intrepid Class, and with the current nacelle configuration, a bit of Nebula class, I'd tend to see this as a late 24th, early 25th Century Intrepid/Nebula replacement.
EDIT 2: Heh, for a "refit" of this ship, after my suggestion of a "Nebula replacement", you could possibly modify the hull spine section, to include a Nebula-type "module" area. A SWACS-configuration might look good on a design like this.