I unhooked my VVIS and I have to say it is a must for all FI cars. I went from 454RWHP to 512RWHP. You can feel the difference just driving the car. The turbos would spool to 16.5 psi, then go down to about 13, they now hold 16.5psi with no problem. Also, don't forget to clean your air filters as I didn't realize how dirty mine were.
Rob
Rob