Fast printing speeds is an exciting and apparently sensitive topic, but we need more discussions like this, hopefully without anybody getting upset.
I do not have a supervolcano, but I can share some of my volcano data.
Max extrusion rate @235 C Volcano PETG
Brass 0.6mm - 24 mm3/s
CHT 0.6 - 29mm3/s not 11x, but it is what I would expect.
I tend to print a lot hotter, so @270 C Volcano PETG
Hardened steel 0.4mm nozzle - 29mm3/s
Brass 0.6 - 36mm3/s
CHT 0.6 - 43mm3/s at about 95% underxtrusion.
Well, my results do not show a whole lot of improvement on volcano, I can definitely see that not far beyond the rates above I get cold filament coming out (temp is OK), so there is a substantial thermal resistance between the nozzle inside and the copper block, so this is work in progress for me.
Perhaps, as it has been mentioned, PETG is just not going to print as fast as PLA.