This table from "fastest lap" demonstrates how little pure numbers (out of context) can tell...
Just try to exclude those results which have been "obtained" on Japanese tracks (these numbers are totally out of line - which is not much of a surprise if one watches some of the corresponding "test" videos) and those results where the cars were obviously driven under different test conditions (wet track, as indicated in the table etc.) and you already get a much clearer picture.
If one then adds some "gut feeling" and focuses on the more reliable test results (also ignoring the Nissan marketing NBR claims which still included in the above table) the picture will be as follows (I am accepting bets on this, BTW ):
HHR: ca. 1.11,5 (GTR) vs. 1.09,7 (GT2) > ca. 2s difference
NBR: ca. 7.43 (GTR) vs. 1.33 (GT2) > ca. 10s difference
0-300: ca. 55s (GTR) vs. 35s (GT2)
These numbers show that Porsche can nicely position the 997TT FL with a performance between GT2 and GTR... There is more than enough room...