I have tried many (perhaps most?) drivers from the 6SN7 / 6SL7 / 6F8G / 6C8G family over the past 3 years. Only the NUs and TS RPs have stood out as great drivers. Really, really good tubes. The C3G destroys them. Not even close. The extra detail, dynamics, extension, clarity is a step change. My audio buddy puts it around 20% vs the TS RP in my WA5 with Takatsuki 300Bs/274Bs. I'm thinking more around 10-15%, but either way, those are huge numbers given that we are already at the pointy end of audio diminishing returns.
The only thing the C3G doesn't do is add any warmth to the music - it is ultra transparent and neutral. In every other department that I can think of, it smashes anything else I have heard. Personally (and a big, fat YMMV applies here) I would not consider any other drive tube.
Tony, how do you compare the Tak 300b to other 300b tubes? I have not heard a 300b in a very long long time. Maybe last I heard one was like 13 years ago with a Rethm speaker and then it sounded glorious.