Need help with pulleys for V-2 SQ S-trim, afraid of overspinning the blower

I'm currently seeing 5# of boost with the Vortech stock pulleys (3.33/6.87). I would like to get 10-12# of boost. I have lying around a 2.95 pulley but I'm afraid I'll overspin the blower in the 1/4 mile. Vortech states that the maximum impeller speed is 50,000 rpm's and at the end of the 1/4 mile the supercharger would be spinning at 52,817.49 rpm's. If I go with the 3.12/7 the impeller speed would be around 50884.62. Should I keep the 2.95/6.87 or go with a 3.12/7? Where can I get the 3.12/7?

Loose belt

Yeah it sounds like the belt is a little loose. Tighten it up and see what happens. Don't worry about overspinning it, no-one else does and they really don't have any problems. but i'd try to tighten it up cause it sounds like you're about 2-3# down unless you live in high elevation.