i think you can push more if necessary without comprimising reliablity. i'm running 7.5psi going to go to 9 ish soon.
depends what you want i guess, its not like a turbo where your boosting max quite quick once you've got it spinning.
my s/c ramps up gradually , starts around 1psi at 1k and hits peak boost around 3k upwards if your at max load with WOT
i guess its what you want and how much you use your car.
but you always want more !!!