My friend, who is an engineer at Roush in Detroit tells me that if you upsize the crank pully then you will increase the belt speed accordingly. Depending on what rpm you will be maxing out at you could exceed the belt rpm limit and have premature failure or wear of your belt. He suggests changing the blower pully to the smaller lightning version (2.93 or 2.80) and then play with a 8" crank pully if you want more boost. If you change the blower pully the belt will spin at the same speed but the blower rpm will increase yielding the increased boost you may want. All you should need would be a belt for a Lightning to make up the difference from the 3.25 to 2.93 pully swap.

I'm gonna try this inthe next 2 weeks so i can let you know how it goes then.