In the original script the BOP was suppose to be about the size of the saucer section of the Enterprise. The original story idea was that the Romulan's had stolen plans from the Federation. CMDR. Hanson actually says something like "our design" upon reporting the ship to the Enterprise. He recognized and identified the ship as the same shape as the primary hull of the Constitution class starship. That being said; I would have to go with option 2 or 3 (actually I think I would vote for 2.5 because there should be a size between the two IMO).