I'm pretty sure an S4 would outrun a stock or lightly modded 350z or G35. I believe they were stating that AWD is at a slight disadvantage on the highway because it is dead weight. AWD pays off in the launch, but once you get moving and the chances of wheel-spin are minimal the AWD car is now carrying the extra weight of the parts making up the AWD system of that particular car that the 2WD car is not.

I haven't looked recently, but I think S4s are actually pretty damned fast. The new ones are a tad heavier than their predecessor, but aren't they rated at something like 400 hp?