that may be true, but i think even the ball & spring type will have some seepage as you near the pre-set boost limit. springs are rated in linear in/lbs and they compress gradually as pressure increases. so in order for a ball & spring valve to be open enough at max rpm to bleed enough pressure to keep the boost down, it must start opening a little before the desired boost is reached.

that's where the electronic boost controllers come in. they do not have a mechanical link between the input pressure and the opening of the valve. they use a sensor to determine boost and a solenoid to open the valve. the valve can remain COMPLETELY closed until the desired boost level is reached, and then openend enough to keep it at that level. that will give you the absolute quickest boost pressure. the more expensive electronic boost controllers even use fuzzy logic to learn engine/boost responses and predict boost pressures to better control the solenoid.