I'm assuming you're talking about the stock twins. I wouldn't turn them up above 18 psi ever. With 94 octane you could probably turn up the boost to about 20 psi and be perfectly ok with your EGTs. But with 20 psi and stock twins....octane and overheating isn't your issue. Anything over 18 psi is just not good for the long term life of your turbos period. You could get lucky and run 21 psi for a year or 2 but the death wine will catch up with you sooner or later. I would even play it safe with 16-17 psi for street and 18psi for the track.