Back in 2001 my brochure on the E46 M3 had a comparison with the C5 in it. Interesting that BMW would do the comparison themself.
The Z06 and the M5 make about the same HP. The Z06 gets better fuel economy.
The only reason for the comparison in this thread is others were claiming the E92 would be faster. It won't be. Even with 500hp it wouldn't be because its still heavier, on skinny tires, and an inferior suspension.
Now despite all that I am not buying one because I don't like the interrior. I also want a car with 4 seats and a real trunk. There is more to a car than just going fast.
Manual gearboxes, the rotary dial of cars.