I just do pve so im not too fussed with pvp style stuff.
What mods should be the better choice for Romulan Plasma beam arrays?
For pure PVE with Romulans, you're best bet is stacking [CrtD]. You'll crit often with a fully-spec'd Romulan, and [CrtD] (severity) makes it hurt a lot. PVE ships just dont move enough to warrant [acc]x2.
As for the original question, these weapons are very very good, and especially good with the 3-pc Romulan set bonus with the experimental beam array and the hyper plasma torpedo. Once you have those together, you get a beam ability that activates a special firing mode on the experimental beam--with buffs you can do ~20k per hit with that mode enabled.
Another thing, try to get a hold of the Fleet embassy science consoles with +Plasma buffs, since they add more base damage to the plasma weapons.