You should use a new chain
We recommend a maximum 32T cassette for optimum gear change.
For a compatible upgrade with the Nova Carbon Ceramic Derailleur GS (medium cage), please check the tutorial video : https://youtu.be/QSZTQPnPy3w
In this version, Nova Carbon Ceramic Derailleur cage is only compatible with the Shimano Ultegra R8000 Series / Dura-Ace R9100 Series.
The Nova Carbon Ceramic Derailleur is NOT compatible with the clutch equipped Ultegra RD RX800 & RX805.