*shakes head* I don't even want to go into how odd some of this information is...

If you're making under 400whp, the 38mm tial is more then you need. Over 400, go with the 44.

If you have a 5psi spring, you can NOT go lower then 5psi, ever. Unless you make a way to divert more gas into the chamber, such as disconnecting the mechanical part of the gate.

Here's how a wastegate works....

It's basicly a valve, opperated by vaccuum and pressure(boost). The spring is set for a certain psi. Under vacuum, this valve is closed, but as it aproaches 5psi, it will begin to open. Once it reaches 5psi it opens all the way. If it cannot open fast enough, this will cause a boost spike, and that settles down once the valve is open. If the gate is not large enough for your exhaust flow, and is unable to pass enough exhaust gases to maintain boost, you will get what is called boost creep. This is when your boost will raise slowly through out the rpm band. If you have a 5psi spring, and you're flowing too much exhaust for it's wastegate, it will raise slowly past 5psi, to 6, 7, 8psi+.

The wastegate itself is very simple. Think of it, as just a valve with a spring. When force of Xpsi is put on that spring, it opens.

Did that help?