A brief assessment of the 997tt's accomplishments:
1. Nearly equal performance of the 996GT2MkII - 0-200kmh in about 12 seconds or about 2 seconds faster than the 996tt.
2. Comparable Ring times to the old 996tt, Gallardo and F430.
3. At least in North America, it costs nearly half of the F430 (incl. premiums) and about 40-50% less than the Gallardo Se.
4. More comfortable & reliable than either of the above.
Given the 20+km length of the Ring, how many seconds would be a reasonable variance from one example of a 997tt to another. Specific atmospheric conditions, tires, driver error, track conditions (repaving, traffic etc.) and build variance. Wouldn't it be interesting to see a 996tt and 997tt go at it together to see which is really faster? Now that would be the ideal test.
I have yet to hear from any actual 997tt owners who feel disappointed. I certainly don't.
Don't let a few published results jade your judgement - go drive one (or anything else you like) and make your own decision.
By the way, the only published time I could find for the 996GT2 was 7'46". Not much better, given it reduced weight, lower ride height, stiffer suspension, 2 wheel drive, etc.
If a few seconds make that much difference to your buying decision, versus all other qualities a car may offer, by all means, go buy something else and be happy.