I am fortunate enough to have experienced both firsthand. A good friend of mine bought an L39 and I've flown it from the rear seat including a few rolls. it flies just like a big heavy RV8. Except the fuel burn rate is breathtaking. We went thru $1200 worth of fuel in very short order.
My best friend just bought a 2014 Cayman S equipped with all the options including PASM. And Torque Vectoring. Its an awesome car. For the bang for the buck value I think the Porsche wins hands down. The maneuvers I could do in the jet, I can also do in my Rv6 for a lot less money... Except for the 400+ knots part