The Explosive Goodbye mod is a suiting option for the Spinning Death overclock because it can help top off your maximum damage with each beam deployed. The DPS from the lingering plasma after the initial explosion can outdo the DPS of the Plasma Trail.
Also, I find that Mini Shells offers a better "general purpose" feel to the shotgun and it allows better utilization of the Minor Adjustments mod, so you can run a more reliable full-auto shotty. Give it a try, if you want.
Breach Cutter's T5 mode is mostly up to preference. Explosive Goodbye might have higher DPS than the plasma trail, but it is only applied after the beam expires. Most things will already be dead by then, and those that are more resistant to it are better off killed quicker with the supplementary plasma trail damage. I also prefer standing inside the beam, so I'd rather not **** myself up, even if the explosive goodbye doesn't hurt too much.
Regarding Mini Shells, it has two huge problems that make it very weak. First, the DPS is awful. The vanilla shotgun just about deals with most trash enemies without much overkill damage. Mini Shells requires at least 1 extra shot for all enemies to die in most circumstances. Second, the absence of stun is a huge turnoff. Keeping slashers, trijaws, menaces, praetorians from hitting you provides a lot of immediate value, which Mini Shells completely foregoes.
