With a completely stock car I would not expect no more than 14-15 psi of boost with 93 octane or she'll be knocking. Witnessed it this weekend on another low mile stock car, knock after 15psi & she was rich on fuel.
Alky or 100 octane is needed to get past stock performance levels safely, 93 of today just isn't what it use to be With good gas or alky you can run 21-22 psi w/ stock turbo.....Some have run much more. (but I feel that is past the efficiency range of the turbo)
I ran a stock car (only fuel pump upgrades) to 8.10's in the 1/8 mile this past weekend on 19psi and 18 deg of timing w/ 100 octane. She has easy 7.80's maybe even a 7.70 in her & still would have been a mild safe tune but would have required couple more psi of boost & a little timing. Launch was limited to 4psi due to Nitto's drag radials. Was able to get me several 1.70's 60' times at that level.
When I say stock, it still has stock air box, 237 fp reg, turbo, dp, cat, etc
All fuel tuning was done with Eric's chip.......