Retarding timing on turbo'ed n/a

[gto7419]

The ej22 n/a is turboed to about 5 psi. I have a wrx fuel pump, rrfpr, and an msd dis2.

Im going to start retarding at 4000 rpm. My msd box gives options from 0 degrees all the way to 15. Im thinking I should start off at 3 degrees?

Good starting point?

Reason for retarding timing - I have been driving around not going above 3k rpm for a while because I believe the car starts to detonate at about 4k rpm. This is either due to the advanced timing, or oil leaking past the the rings at increased crankcase pressure. - Either way, I think it makes sense that retarding the timing slightly would help...

I also want to switch to a slightly colder plug - any recommendations?