The test you are referring to (996tt Kit) should not be the reference. I believe Porsche was pretty mad at DCX for screwing a "SLR development engine" into a ordinary SL55, take it to Nardo (AMS test) and beat cars like the GT2 in acceleration.

I think for this particular test Porsche also supplied a very healthy engine - at least 500hp in my opinion

The 997tt (tip) will be substantially faster than the 996tt kit manual, no questions about that.

OAB