I figured that the Romulans would refit the D7s they traded with the Klingons (during their alliance in the 2260s) and refitted them when they learned of the Federation refitting their Consitutions and the Klingon's introducing the K'T'inga-class Battlecruisers.
But eventually it didn't work out and they used that knowledge to create a true Romulan Warbird, the Belavis, which was further evolution of their ideas on the refitted Romulan D7s and supposed to keep them competitive against the new Federation Excelsior-class starships (as well as the K'T'inga, which proved to be superior than they anticipated).
As they learned of the Federation constructing the Ambassador-class, they introduced the Verterax-class. It's believed four of these ships participated in the Battle of Narendra III, where it shown to be slower in turning than the Ambassador, but the new Quantum Singularity drive kept it in the fight longer and eventually won.
Though it's victory over the Ambassador-class was regarded as a victory, the Romulan leaders felt that they need a superior starship, and that eventually lead to the D'Deridex project.
Well that's my take of the Lost Years of the Romulan designs. Though it really was designed on the spur-of-the-moment than really thought out, I trust you liked them.
I especially like the Verterax and Belavis classes, they look really cool.
The only thing i would change is the sphere bow of the temporum, i would have made it a bit more angular. I understand they are supposed to be refitted D7s but i think it would look much more romulan if it where a bit more angular shaped.
Maybe if it had some kind of wedge shape, it would look good also, just a thought.