It is really a question of gearing. Did the GTR jump hard, let off then get back on it??
The reality is, that M6 could be making something like 530whp/500wt stock, has a 7 speed dual clutch, and has an additional 200RPM suggesting a broad power band up top. Both have excellent gearing and make power until redline, but the GTR's 3.70 gear allows it to be in 4th gear by 99mph. The M6 doesn't hit 4th until 105-110.
To me, this would suggest the GTR would simply jump out and stay out until it got to it's wider ratios post 100-110mph.
As far as dig racing and trap speeds you can't really argue a point with that and use it as a concrete fact. They are variables, in the sense that the conditions, driver, tires, track prep vary.
What is fact, is the GTR hooks up and the M6 does not from a dig. Both cars have trapped low 120's in the 1/4, albeit the M6 doing it while only powering two wheels through the 1/8th mile.