None.
It was no more than a theory - a long time ago - that the resistance of the R8 coils could provide a better spark. But in practice, there's no real difference.
They're a bit cheaper than the black top GTI coils, and red. That might have helped the theory gain a bit of momentum for a while, if you know what I mean.
The only way of guaranteeing any 'performance gain' would be replacing knackered coils with new ones. Regardless of which were red or black.
Unless your existing coil(s) are knackered, in fitting a used set you stand to gain zero, or even a misfire you never had.