In "United" the Romulan prototype ship has a warp drive that appears to be able to go close to warp 5. In "Balance of Terror" Scotty clearly states that the Romulan Warbird does not have warp drive. What gives? How come a prototype from 2154 has a pretty advanced warp drive, but a Warbird from 2266 does not? Has this ever been addressed before? Was the cloak in BOT such a power drain they could not have a warp engine?