Saw an older one at VIR in August and he was smoking fast. Coming out of the Hogpen I think he was accelerating to over 140 by the time he passed the garages, seemed to literally slingshot as if pulled by a giant rubber band.
But as for the drivers, I see it this way - a top level F1 driver is much more likely to extract max performance out of a cup car, and get out there in front. The opposite is simply not true - if you aren't weaned on aero cars from the beginning I doubt you can maximize a F1 car the way Alonso, Hamilton or Vettel can.
I'm not saying this with any sense of superiority, I've been enough on track to know my own skills don't even register on the scale...
The same goes for WRC, which requires a very particular set of skills. Kimi did horribly in WRC, but he still has gobs of speed in F1.
2004 Z4 3.0
2014 X1 28i ED
2015 F80 ED in June