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around 1.6 or so is as much as you'd want to go on the standard map sensor - as has been said above a new map sensor is needed after that but you'll still have difficulty targeting over 24psi in some ECU's.
You would be looking at aftermarket boost control systems after that and you can still keep the stock ECU doing fuelling and timing without any hassles.
I'm running 1.7 peak, holding 1.5 to limiter. I asked for the boost cut to be removed during mapping (std 255kpa map sensor doesn't read high enough for me)