But the skidpad rating for the Z4 M is only 0.89 Gs (vs the 370Z's 0.98). You then have essentially the same car except for the 370Z having significantly better cornering ability. Given that significant difference, I'd put money on the 370Z trumping the Z4M.
Looking at that list again, a more interesting comparison is the Porsche Cayman S...a car that Nissan itself pitted the 370Z against. The Cayman S pulled an 8:11 lap time. So, I'd put the Z right in that range. Given that Cayman S's time, I agree that the stock 370Z probably couldn't 'best' 8 minutes.
Suffice to say though, our 370Zs are in good company...especially when we paid <$40k!