Tokico is a quality brand of shock. While I've not used them on a C4, I have used them on a C3 to replace the OE FE7 shocks on an 82 CE. They were an improvment in ride with handling staying about the same, but I would have expected that with technology which was at least a decade newer. I've also had Tokicos on a GM front driver replacing worn stock, base-level parts. They were a significant improvement in ride and handling there.
That said, I think the earlier statements that: a Tokico outperforms a Bilstein in every category and that a lot of road race cars used them are false and cannot be documented.
It is possible that the Tokico for a C4 may outperform a Bilstein in some situations but it would depend on the level of suspension on the C4 in, how the Tokicos are valved and what the driver expects from replacement dampers.