Were all the cars standard? On similar tyres? Exactly the same skilled drivers?
If you google it you see forums posts of Boxster drivers boasting about how they beat a 350z, and vice versa on more Nissan branded forums. Both are very closely matched in terms of stats, so doubt one would completely annihilate the other and it would be a close run thing, all things being equal.
Didn't look too scientific, I had a small boot against my mates coxster but as I said can't really take him as an example as most Porsche owners would shoot him in the face Also his is the 2.7???