This Depends on the Supercharger Setup used, Power is relevant to a lot of factors including your engine as well as the efficiency and amount of air flow (CFM), not exactly something that can be calculated just based of Boost Pressure (PSI). Hence on a smaller older blower you may overdrive the blower to get more CFM, while a larger or more efficient blower can push more air at the same boost levels and be capable of delivering more power.
That said, the dyno records suggest a mere 3PSI or from the SC14 you can see around 25-35 WHP (Around 35-40 HP at the Motor/Crank). 8 PSI Should give you around a 50% Increase theoretically.
For High power applications we suggest our M1 and larger setups.