I don't have the measurements to prove it but having spent 3+ years in my 1998 and a month and 1,000 miles in my buddy's 2006 Cayman S, I think the 987 Porsche has a lot more room inside than the NSX.
The NSX has much better sightlines and far less blindspots but head, shoulder and leg room is much, much better in the P car.
And the in door storage pockets are bad ass.