This newest Whipple is the same displacement as the existing Whipple and, in fact, uses the same case. Whipple has come up with a new rotor design that allows for the same boost pressure with slower rotor rpm's. A challenge for the SC manufacturers is that more boost is obtained by increasing the rpm of the blower (duh). In order to achieve this additional speed/boost, you need to drive it with a smaller pulley and, ironically, you will have less belt wrap (surface contact) but higher HP draw. As such, one of the advantages of Whipples new rotor design is that owners can run, for example, 21 lbs of boost with the same diameter pulley that today produces 19lbs of boost, thereby achieving better belt contact area and mitigating slipping issues.
Perhaps more relavant to the broader GT community, if your objective is 19 lbs of boost, you can achieve this with one pulley size larger in diameter as compared to what is available today. As belt slip is not currently an issue (with the 19lb pulley), the real advantage will be that the new blower has the potential to be more efficient (less HP draw for equivalent boost) and slightly improved IAT's.
My view is that for those people interested in 21 lbs of boost or more, the new Whipple may be worth waiting for. For those that intend to run 19 lbs of boost with a 91 octane tune, it will be interesting to see if the differences in the real world (if any) and to compare this against any potential price differences.