Gas for AoE tagging ([Energy Generator] and [Synth Deconstruct]). [Fast Hands] for less downtime in firing. 3x Vigilante mostly just for the set bonus. There's not much you can really do to crank this, [Verglas] already applies status insanely fast, so more fire rate kind of just means more reloading downtime, and more status just isn't very helpful. [Sinister Reach] does not work, otherwise I'd probably use it.

I generally prefer this to the [Helstrum] tho it limits your range a tad (24m when attack range is 30m). Helps that it also instacaps cold too and deals a lot of damage (which obviously falls off in high levels but is relevant even then sometimes).