Boost refDC settings seems good to me,
have a look at the wastegate valve, a leak is often causing late spool. This wastegate-assembly is easy to check and maintain.
Also check the N75 valve, if it's leaking, the control pressure rises even with 100% refDC.
late spark should'nt causing late spool this much, resulting higher egt is even better.
Activate the EGO closed loop control, you are running quite rich.
regards