It's hard to say, either one on their own would certainly have a big effect on the handling,
and in the 911 case moving the engine from rear to mid they will get the benefit of both
But just based on the cost to do something like this, I would have to think the driving force behind the decision was vehicle dynamics,
Then I look at that rear diffuser, and I change my mind
What ever the reason for this change, it will be interesting to see how the car stacks up with the competition
they've done pretty good up till now with the engine hanging off the ass end of the car.