I can't say that I've ever actually checked but if you're referring to the fuel rail pressure dropping after you turn the car off, I'm hardly surprised.. without the fuel pump functioning it's always going to drop off.. it doesn't necessarily mean that the injectors are leaking.
Ideal fuel pressure is a pretty indepth conversation if you want to get into the inner workings of fuel injectors, I will say that if 3bar fuel pressure will flow your required power that's probably where you should leave it.
You can sometimes gain some efficiency in the spray pattern with higher pressures but the significant down side is the increase in 'dead time', that is to say the time between the ECU sending the signal to fire and the injector actually responding and opening all the way.
Increased dead time will lead to a disproportionate increase in duty cycle required to keep the required air to fuel ratio, this non-linear progression of duty-cycle to actual volume of fuel delivered due to increasing dead time wreaks havoc with temperature or voltage correction. For example if your intake temperature compensation adds 10% (numbers are examples) more fuel for every ten degree drop in air intake temperature but you're running at the upper limits of the injectors capability that additional 10% duty cycle might only translate into an additional 5% of fuel in the real world, leading to a lean condition and potentially the end of your engine.
All injectors are not created equal, the later generations of bosch or siemens injectors aren't even comparable to the earlier generations like the standard starlet injectors, they are far more tolerant of increases in fuel pressure, so much so that the latest generations will quite comfortably function without significant detriment at 130psi flowing 70% more than their rated flow