As I thought about it, it didn’t seem fair for me to ask what you are basing your conclusions on without providing at least a couple of sources myself so here goes…
370Z TESTS….
RoadandTrack.com -- New Car Search - Full Test: 2009 Nissan 370Z (1/2009)
Skidpad: 0.97
Slalom (700’): 71.4 MPH
0-60: 5.1 seconds
0-100: 12.8 seconds
¼ Mile: 13.7 @ 103.6 MPH
Comparison Test: 2009 Nissan 370Z vs. 2008 BMW 135i
EDIT: Now that I've read your reply, I see we were pretty much thinking alike!
Skidpad: 0.97
Slalom: 69.8 MPH
0-60: 5.1 seconds
0-100: ---
¼ Mile: 13.4 @ 104.6 MPH
NISMO 350Z Tests….
Follow-Up Test: 2007 Nissan Nismo 350Z
Skidpad: 0.91
Slalom : 70.0 MPH
0-60: 5.1 seconds
0-100: -----
¼ Mile: 13.6 @ 103.0 MPH
RoadandTrack.com -- Cover Story - The Fast & The Frugal: Nissan Nismo 350Z (8/2008)
Skidpad: 0.96
Slalom : 69.4 MPH
0-60: 5.3 seconds
0-100: -----
¼ Mile: 13.7 @ 102.3 MPH
Obviously, testing differs with any number of variables but based on the above (as well as other articles I’ve read, it looks to me like the 370 has an edge in the skidpad, in acceleration and is almost in a dead-heat as far as the slalom goes…the 370 seems to have a nice edge in braking (60-0) too although I didn’t list those numbers.
If someone is shopping a 370 compared to a NISMO 350; I’d say the decision is going to have to be made on issues other than the raw numbers and lets face it, regardless of which vehicle you give the nod to based only on the numbers, the numbers are so close that any “advantage” can easily be erased by driver skill (or lack thereof).