As a start, have you tried printing with the generic profile that worked with the stock nozzle? From there you could try adjusting parameters one by one, e.g. first increase max flow to the point where you see problems.
If you tested the stock nozzle with the generic profile and the Obxidian nozzle with the Bambu HF PETG profile, it is quite possible that the problem is not in the nozzle but in the profile.
When I tested different HF PETG brands, I saw very big differences in quality at higher speeds. I haven’t tried Creality, but it is well possible that it needs quite some fine tuning to print acceptably.