Want to check the boost I am getting on my early 94 WRX (saloon with TD05 turbo and W6 ECU). Which according to Scott at Polar Performance's website is "WRX 1993 - Sept 1994 : 11.47psi"

Got a mechanical boost gauge it's seeing up to 10-10.5 psi on the gauge but not too sure how accurate it is. I have a second gauge I can plumb in to check the first gauge accuracy. But a couple of questions.

At what rpm should I see max boost?
And does anyone know of anything I can temporaily use a one way valve so the gauges hold the peak boost readings