24PSI???
Tarzan is 24 PSI really required?? What application are you using it for, drag racing or mountain riding?? I am just curious, ..I can understand 24 for racing but for practical daily reliable riding, ..wow! Is this on your Big Engine??
To answer your question, I don't have first hand experience with the Powderlites O-ring head shim. Going back a few years, there were some guys trying to run 22 + psi on their Yammies, they had a Shop machine cut an o-ring groove into the block, then place O-rings into the grooves. Seems to me they had some success but also some related issues, perhaps they can add their input for you.
Makes for a lot of dynamic compression when spinning high rpm's with 20+ lbs of boost. Reducing your static ratio down to 8.5 should definitely help.
Noticeable around here these days, guys are reducing overall full load boost and opting for a higher static compression ratio for overall performance gains with a crisper throttle response.