I don’t have direct experience with GRF90 but I have had Canterbury SE, GR, Kensington SE and Yorkminster SE in my system (same room). On paper (though they drastically changed the look), the Yorkminster SE is the previous version of GRF90. The Yorks definitely have a cleaner, less lush and less rich sound than the other Tannoys - which I found harder to engage with. The rich, vivid midrange of the Kensington and Canterbury is what drives me to those models. Note that besides the 12" driver being unique to Yorkminster / GRF90, these models also incorporate rear reflex porting compared to the other Prestige Tannoys’ simple vented cabinets. This may contribute to the sonic difference as much as anything.
Kensington may actually have the most "beautiful" midrange in some ways, but the image size is larger and has more impact with Canterbury. I also didn't like the DC10A, which uses the Kensington 10" driver in a modern-style reflex ported cabinet.
What the Yorkminsters did spectacularly was bass - quality, quantity, impact, and extension. On paper it’s only 24 Hz vs. 28 - 29Hz, but in room it sounded like a huge difference.
As far as the Canterbury SE vs. GR - there is obviously much of the same sound but the SE was a little dark on top; the GR fixed this and incrementally improved detail & transparency to boot.
