I run 15psi with a t04e 57 trim on my stock motor no problem and i've been running 15psi from my old smaller vf39 for some time. With the right tune you can go above 9psi. Why not just go with a stock z6 block so your compression is 9.2:1? The higher compression doesn't have anything to do with the reliability of the motor. It has to do with how much power your are limited to with the octane gas that is available to you. If you can get it down to low 9's then you can run plenty of power on 93 octane.