Another important factor that no one on any car forum seems to address is DA. I remember that one guy about a year ago claiming that his C6Z06 ran 10's and it was stock with tires. Yeah, it did, but it was at -800 feet DA. Those racing conditions are so rare, that they are next to impossible to duplicate.
Someone may live where their DA on that certain day, at that track, at that time of the day may only be 3500+' above sea level and they may not get very good times.
Here is a little converter:
http://wahiduddin.net/calc/calc_hp_dp.htm
So for example, right now it's 61 degrees, Baro. is only 29.69, dew point is 34* and we are at 1,200' above sea level. So, the density altitude is 1963'. Not horrible, but the best we may get out here in the winter is in the 1200' range. If it gets too much cooler out, say in the low 50's or so, the track starts going away and that new-found power is wasted.