Trust me, its easier to squeeze better times out of a Z06 than an E46 m3.
Think about it this way. The best Z drivers are squeezing 112+ MPH out of their traps, whereas an M3 will run a 13.1@104-109.
The margin for performance increase is much larger in a smallblock V8 than a small 6.
Again, even though they compare (FR, high power), I don't think people should even compare the two. The ///M3 was bred for twisty mountain roads while stopping for a nice coffee on the Riviera. The Z06 was designed to be an all round good drive, with an emphasis on the devilish V8 thrust.