981 Cayman S vs GT350

ZCanadian

Today's NISMO Z compared to a 10-year old Cayman S:
http://www.zeperfs.com/en/duel4693-1326.htm
(keep in mind, the pricing would have been new, and is European list).

Assuming the car is still doing what it should, the Cayman out accelerates and out-brakes the 370Z in almost every range. It's lighter (not surprising, as 10 years ago the safety features were less, as were some of the comfort items). But they are no match for a more modern true sports car.

The newer Caymans (the 981s you originally mention) are considerably better.
Today's NISMO Z vs outgoing generation Cayman S
http://www.zeperfs.com/en/duel4693-4557.htm
I've toyed with them on the track with my car (not the Z) and they are truly impressive. I can still take them but not as easily as the older generation cars, and depends more on on how they are driven. And those drivers probably have a far more comfortable trip to and from the track, or daily driving their Cayman than I do my ride. Driven well, they'd eat a stock Z and spit it out their tuned tailpipes.

The newest, 718 with the turbo 4, is really just as good as the last generation on a race track.

In the end, the question is really what you want out of your car. Reliability? Bragging rights? Looks? Comfort? Tech? Safety? Value? Economical operation? Practicality for daily driving? Back seats? Cargo space? Quarter mile speed? Road course or Auto Cross performance (economical or otherwise)? Doesn't have to be just one, but it pretty much cannot be all of the above in top priority.

It is hard to beat a Porsche for a lot of things. But as they age, it gets harder to keep them doing what they do best, and harder to justify putting the money into keeping them up to the standard you'd like yours to be.