There is a lot wrong with this! Compare apples to apples.
First, a good SCT Dealer can get you very close to perfect with any mod combination with the file they build for your car via chip or hand held tuner.
With the Extreme Tuner package and XCalibrator hand held tuner, you do not have the ability to data log, clear codes or tune without a PC/Laptop.
With the Extreme Tuner package and SCT 9100 hand held tuner, you can clear codes but cannot data log or tune without a PC/Laptop.
With the Extreme Tuner package and XCalibrator 2 hand held tuner, you won't be able to tune without a PC/Laptop.
Comparing the Extreme Tuner Software package with the 9100 or XCal 2, the SCT hand held tuner is far superior to Diablo hand held. It gives you a lot more flexibility than what you can do with Diablo. Change your MAF and with the extreme tuner software, you can do it yourself. With Diablo, you have to download the file.
The pro racer package is a step up yet from the Extreme Tuner package. Tuning the 2005 Mustang is the perfect example for comparison. Why is Diablo having so many problems with their tuning of it? The SCT dealers I know of are not having any issues and are finding power.
BTW an SCT vote here.
Some of the best SCT dealers:
http://www.blueovalchips.com
http://www.modulardepot.com
http://www.modularpowerhouse.com