Since you didnt list any engine managment you should start with 15 psi of boost. The gain is how you set the the boost threshold. If you set it to the highest setting then it will spool the turbo up the fastest and make the wastegate be the most responsive. I would play with the gain until you are happy with the way it spools up (you want a smooth transition to boost) and then make sure it can hold the 15 psi of boost you want after that. If you get a reflash then you can increase boost because you are adding more fuel and more timing amung other safeguards. Just be careful and dont raise the boost to high. You have the mods for more power just not the reflash to handle a bigger boost increase.

 

I am finding that my car acutally spools a bit faster the way it was reflashed (ecutec) without the boost controller (I have a greddy profec 1st gen). My spool up seems to now be 500 later with the profec. The upside is the turbo holds the boost fine all the way to redline. I have a vf22 and supporting mods.