My firtst encounter with the Romulan BoP were the AMT model kits (before
I saw the episode) and for some unconscious reason I already felt the model (option 3 if I remember correctly) to be too big next to the AMT Enterprise.
Maybe it's the lack of truly interesting exterior features (like a hangar bay?), the vessel looks rather compact and more like an oversized shuttlecraft compared to the Klingon Battlecruiser or the Enterprise
For me, option # 2 is the one that feels
right. I wouldn't really mind option # 1 but anything bigger than # 2 looks odd to me.
Just came across this great source with descriptions and lines from the original "Balance of Terror" script
Here, the Bridge of the Romulan Bird of Prey was originally envisioned to be a "cockpit"...hmm...sounds like the BoP was rather intended to be some kind of stealth bomber (coming from a mothership?).