Greg I assume this is the last year for the C6 Z06 and if so and you wait for next year you'll not find one
But 2006 MY Z06s can be had now for a good saving though the 2008 has redesigned trannie and shift patterns so it would be the year to own.

No one can tell if car was tuned unless they downloaded the PCM and compared it to a stock flash calibration but if you lock the PCM with LS2edit they would not be able to do the download.

Tune will really wake the Z06 up for I think GM had degraded the true performance within the tune.