The Romulans had to of had a warp drive, otherwise they would be essentually a meaningless fourth rate power at best.
The events seen in ST: Enterprise would make no sense without the Romulans possessing the means to travel reasonable quickly between star systems.
... as well as Klingon ships outfitted with Romulan cloaking devices
Was it ever clearly stated that the Klingons obtain their cloaking device from the Romulans?
During TNG, starfleet could on occasion detect cloaked Romulan ships, but (iirc) couldn't do the same with cloaked Klingon ships. Suggesting that Romulan and Klingon cloaks work somehow differently, and are two separate inventions.
The Dominion also possessed cloaking devices aboard their ships, and obviously didn't get their's from the Romulans.