Wowzers! Well done, man!
I could see the first Study Model being a concept ship- it tried out all the technology going into this concept. Maybe a few were made and the project shelved for a while. The originals carried on menial support assignments. Then Starfleet decided to revive the ship concept, and along comes your design!
What I don't like (and I wouldn't expect you to change your baby here), are the impulse engines- I would make them a wee bit larger (just a bit though), the nacelle cowlings, and the end caps on the nacelles- red and recessed like that just don't do it for me.