well 5.2 to mee sounds about right, considering no magazine ever got a 99+ to d better than 5.5. But the quarter mile does sound high, but most magazines underestimate 1/4 times when therre are no true published times to base it on. But the mph could be accurate maybe more like 105.
Anyways sites like these are just making guesses for the most part. On a side note about the car and driver stuff. They specifically say in the back of their magazine, that unlike motor trend and the performance oriented only magazines, that they do not powershift or completly rag the cars that they test. They test them how most of population would drive. Relatively easy launches and smooth shifts that are not banging gears.
If you compare most magazines to car and driver i would say that about 75% of the other magazines have faster numbers for the same car that c&d tested. But car and driver are the ones that got some ungodly 12.0 out of a z06.