Your assuming the quicker C6 is all due to the tune but your forgetting the bad tune could have made the other C6 even slower.

The good tune clearly made gains from a true custom tune that touches all functions of the PCM and assures powertrain performs well from startup through PE to WOT.
I do NOT just tune for WOT and as you know its as important for engine to perform well to get to WOT as those who are just tuning for WOT.

So yes I touch everything that I can when tuning but again it is the OBD scanner recorded data I spend as much time analyzing as time to do the tune as that data tells us exactly what engine needs to perform at it's best.

Clearly the shop that tuned the other C6 knows nothing about tuning and I'd bet they do not even use a OBD scanner and custom tune to that car and the driving habits of the owner.