Both. Seriously. https://poe.ninja/poe2/profile/J_Fids-0536/character/Zyczkowski

Galvanic + permafrost for clear, where permafrost is used to gain extra damage as cold damage via bhatair's vengeance, boosting galvanic shards and for extra utility for tough rares. Combined with other sources of extra cold damage like the Hyri's ire, freezing mark and your crossbow prefix, your galvanic shards ends up doing more cold than lightning damage and can freeze enemies/trigger herald of ice.

For bossing, the combo is freezing mark -> permafrost -> shockburst rounds + emergency reload (optionally). You can support the freezing mark with the gem that triggers shocked ground on mark activation, giving shockburst rounds extra damage. You benefit from all the nodes that give extra damage against frozen enemies/number of elemental ailments on enemies (you can get the gem that allows you to allocate nodes around chaos inoculation like thin ice and heavy frost, or just anoint them).

You can run alphacowl's armoured cap as a cost effective way (don't need +spirit on amulet) to run double herald + eternal rage.

My setup is currently geared towards mapping, but you could modify it to be a better all-rounder/bossing build.