I've got a WhisperFlo WFE-8 with a 2hp motor and 1.3 service factor. I'm looking at installing a 3.5 sfhp variable speed motor, the AVSS3 by Nidec. I'd like to be able to take advantage of the additional horsepower, even if momentarily. Should I buy the impeller for the WFE-12 and install that? Do I need the diffuser from the WFE-12 as well?