Another question for bypass/blowoff valves

[Makahveli]

For forced induction air I've done research and maybe mistakin but it seems that if you drive a 5-speed manual that a bypass or blowoff valve is reccomended, if this is so for us guys just running 6psi what spring rate should we be looking forward to getting? Like when the throttle is suddently close from WOT Does the boost almost double since it has nowhere to go? I'm not looking forward to upgrading pulleys anytime soon, but am I to only get a valve when going over 12 psi? I don't have access to a boost valve yet, as I don't think its needed or am I wrong?