A GT500 would kill a 370z in a straight line and it will beat it in a long twisty roadcourse like VIR, Big Willow etc too. I remember the old 06 lightning Lap where a GT500 that suffered major ignition problems was still faster than a well driven 06 350z by a second and a half [GT500 3:11 to the Z's 3:12.5] Teh next year the GT500 was just a few tenths off a Porsche 911 TT and about 8 secs faster than the 350z time from the previous Lightning Lap. On a highway roll its lights out.
The GT 500 should be faster then the 370z as well imho. I highly doubt a 370z is 8 secs faster than a 350z on VIR and it would need to be just to approach the GT500's time much less beat one on a track like VIR. Short tracks it will have a chance as outright speeds are less critical.
Also the Cayman S was 4 secs faster than the 350z in that same 06 Car and Driver Lightening Lap test. GT500 was 4 secs faster than the Cayman S. The 370z is as fast as the old Cayman S. The GT500 is not a handler like the 370z but, "track dependant", it can beat a 370z.
06 Lightning Lap head to head. Z vs Cayman S vs GT500 to name a few
07 Lightning Lap GT500 fast lap 3:05.9