just to add my $0.02...tires make a HUGE difference, and while 10 seconds is a stretch, 5-7 seconds is not. For those who have used R compounds, the difference is SOO dramatic compared to even the best Michelin Sport tires on the market. The speed one can carry through a corner is breathtaking in comparison. If you put a set of Cups on a CGT, you would probably see several second improvement to say the least. Also R compounds work well with a lot of heat in them, when street tires easily overheat after a few laps.

I do find it interesting that more OEM's are starting to put R like compounds on their street cars. It certainely makes things interesting, but more difficult to compare on an apples to apples basis. For example, I can take a car with almost 100 less hp than a close competitor, put a set of hardcore track compounds and be tearing up cars that are way out of it's league.