Radiation is strongest against murmur Indifferent Facade, Necramechs and Archons.

Corrosive is strongest against Acolytes (without strip), Sisters/Liches, Sentients (e.g. Archon missions pre-archon confrontation) and Culverins (without strip). Can swap [Accelerated Isotope] for [Pathogen Rounds] and rearrange [Primed Heated Charge] to make Corrosive Heat, OR swap [Primed Heated Charge] for [Pathogen Rounds] to make pure corrosive, and use anemic agiliity for more fire rate.

You can also make a mix of Corrosive + Radiation to hit both types of enemies hard by swapping [Primed Heated Charge] with [Pathogen Rounds] and keeping [Accelerated Isotope].

External fire rate sources make [Noctua] feel much better, since it has infinite ammo and zero reload:
With [Accelerated Isotope] and [Lethal Torrent] as well as external sources such as Arcane Velocity (+120%), [Reinforced Bond] (+60%), [Afentis] (+20%) and [Amalgam Furax Body Count] (+45%), we can boost the base 1.5 fire rate to a total of 6.975.

External Critical Chance boosts can further boost primary fire [Noctua] damage:
Primed Pistol Gambit (+187%) with Secondary Outburst (+240% CC at x12 combo) gives 158% CC (on primary fire) and 237% CC (on alt-fire)
Adding Arcane Avenger gives 203% CC.
Adding secondary crit chance shards could give up to 260%CC (with 5 crimson) or even 315% CC (with 5 topaz)