Normally I find that the unique version of any given weapon is clearly superior to the normal version with mods (e.g., Ratslayer vs. a Varmint Rifle with scope and silencer mods), as it tends to do everything the mods do and also deal more damage. Oddly, though, I'm getting the impression that a modded 9mm SMG may actually be more useful than Vance's 9mm SMG. With the firing rate mod, my DPS (with Guns skill around 90ish) is about 220, which is higher than both Vance's 9mm and even the 10mm SMG. Am I missing something here?

(Of course, both Vance's 9mm and the 10mm SMG have higher DAM, but they're still so low that they're only really useful on basically unarmored foes. I pull out higher-DAM weapons or an Avenger minigun with AP ammo against armored foes, and basically use the one-handed SMGs against Cazadores, which attack quickly, so higher DPS = better as far as I can tell.)