OFC or OCC magnet wire?

[Zhangliqun]

Does anyone make these in the tiny gauges we use? And would it even make a difference?

[Helmholtz]

And would it even make a difference?

The copper used by Elektrisola has a purity of 99.95%. Not much room for improvement. Extra high purity copper (99.99%) has a resistance lower by maybe 2% or 3%.
The main benefit of OFC is increased flexibility.