MKSGR
I agree, comments by G Schmirler re the CGT being quicker than the 542hp 1420kg 996GT are not helpful and I believe inaccurate. My guess is he had his "selling CGT engine packages" hat on that day - I think he got confused between a standard CGT and one with their 690hp Kit.
Look at the evidence, AMS tested the 542 GT2 0-300 in 28.5s, they also tested an EDO 996GT2 with the same engine kit and the 0-200kph was almsot identical.

The CGT was tested 0-300kph in 34.2s

Checkout that video above, my car running 520hp was neck and neck to 130mph, on the following straight (1.4miles) I managed 193mph before the timing beam and the CGT managed 195mph
http://www.pistonheads.co.uk/gassing/topic.asp?t=314544&f=133&h=0
I had a data logger on my car for that run and two people in a 993GT2 arched 520hp car did 0-300 in 34.3s

The CGT looks spot on for the tested numbers.

The 997tt takes 40s which again looks right for 480hp - wait for the road tests, the Cargraphic RSC3.8 (618PS) will dip well below 30s, my guess is 25s dead.

What one must remember when relating hp to acceleration is the shape of the curve - the naturally aspirated accelerating through the gears in their "power range" say from 6500 to 8000 in the CGT will have steep power curves with around 80% of peak @ 6500rpm cpmared to the turbo Porsches which will have over 90% at the 5500rpm start of the "power range"
This is what makes turbo Porsches accelerate much faster than the bare peak hp numbers