the Phat Cat is typical Seymour Duncan tone- lots of midrange definition & superb overall clarity. if you are into such requirements, the Phat Cat is the way to go, it is also one of the most affordable humbucker-sized P-90 on offer off the shelf.
the P-94, when i heard one in use, is what you'd hear coming from a good Epiphone Casino- all the fatness but nothing too protrusive in the upper frequencies. jazz cats might like this one especially the neck unit. it responds very well with mild drive.
on the contrary, if what you wish to propel requires lots of high gain/ upper drive levels, the Phat Cat does better. the Phat Cat has more Jazzmaster like pickup quality to it. the reason why it's my preference 8)