The latest issue of german car magazine auto, motor und sport has a comparison test with various tuned 997 Turbo in it. Judging by the achieved test figures, I have to say that this is exactly what I expected. Huge disappointment and not worth risking the warranty, not to speak about the huge cost.

Just for comparison:

997 Turbo Stock
0-200 kph in 12.3 sec.
0-250 kph in 20.7 sec.

997 Turbo 9ff (535 HP)
0-200 kph in 11.2 sec.
0-250 kph in 18.4 sec.

997 Turbo Gemballa (550 HP)
0-200 kph in 11.6 sec.
0-250 kph in 19,8 sec.

997 Turbo Speedart (530 HP)
0-200 kph in 11.8 sec.
0-250 kph in 20.2 sec.

997 Turbo Techart (580 HP, modified or no VTG?)
0-200 kph in 11.7 sec.
0-250 kph in 19.8 sec.

997 Turbo Wendland (530 HP)
0-200 kph in 11.7 sec.
0-250 kph in 19.8 sec.

With the exception of the Techart and maybe Gemballa, all cars had actually only a modified exhaust system (incl. cats) and a different motronic programming.

It is well known that the standard turbo chargers aren't good for more than 1.2-1.3 bar, so more than 550 HP without heavy engine/turbo chargers mods isn't possible right now.
It is also very interesting that ams says that all cars lost the advantage of the VTG technology after the mods, mostly the almost missing turbo "hole".

This test confirms our recommendation from the past: WAIT with engine mods, Tuners still have to get more experience with them. Unless you want to be the guinea pig for a lot of money and without any substantial results.

Porsche actually did a very clever job by introducing the VTG technology, they made life much more difficult for Tuners to gain extreme power at "low" cost.
We predicted it before but apparently nobody believed us.

I wouldn't be surprised to see the same disappointing results from modded suspension setups, the first numbers from the test (outside temperature was 6*C btw, to the advantage of the engine of the tuned Turbos...stock Turbo has been tested at 25*C) already give a short glimpse in that direction.