Nurburgring is a high speed track, the record setting GTR was as fast in the main straight as the Corvette ZR1 (around 180mph). The stock GTR is far slower when compared to the ZO6 and 911T above 100mph.
I dont think Nissan used racing tires but do think that they had the boost turned up. Also notice that early reviews had the GTR perform better than more recent reviews.