Buyers with young children (and that's a big % of the new-Porsche-buying demographic) will remain tempted by the 911's small back seats, even if everything else between the 997 and Cayman X were equalised. So maybe half of them would go for the 997 instead, just to have the flexibility of being able to transport their kids (I'm thinking of two-car families here in particular... where buying a Cayman means you are totally dependent on the "other" car to move your kids around).

Everyone else would probably go for the Cayman X, given that it's has superior packaging for a dedicated sports car.