As above, how much boost you can run isn't just about compression ratio. Fuel, cams, spark angle etc. - all of these factors affect it.

However, 20 psi on a T34 will typically net you around 300bhp with these pistons - so unless you're planning to get a pukka head done, you won't be running 25 psi anyway. You should figure out what power you want, rather than what boost you want and then design the engine around that.