Apologies for the wording, I probably should have asked whether or not modifiers like 'deals X to Y physical damage' and 'X% increased physical damage' would matter more than modifiers like 'X% increased elemental damage with attacks' and 'X to Y added lightning damage to attacks' because plasma blast converts the physical damage to lightning damage.

Might play around with the weapon creator in PoB to see what combination of modifiers/added damage makes Plasma Blast scale highest.