One area of technology where the Romulans are quite good with are metaweapons, doomsday weapons capable of inflicting massive damage and/or subverting other powers' weapons...after using the Sunseed technology, the Romulan Praetorate launched a weapon that would have made Sol hyperflare and destroy our solar system, and would have been happy to do the same to the Qo'Nos system; the Tomed incident saw an "accident" with a single singularity drive-equipped Romulan warship annihilate outposts scattered possibly across light-years...
There's evidence to suggest that the Romulans did well against the Borg. The Verithrax, a single ship, was able to destroy the Borg vessel attacking Ardana.
In what books or stories did these events occur?
And do we know if the Verithrax survived the engagement with the Borg?