Can't comment on differences with your 3.6, but for my 3.8 I have used Procal, Flashcal, Flashpaq, and Diablo InTune at various times. Tunes from the Diablo had a better 'butt dyno' performance increase than Flashpaq. Whether it was shift points or HP or whatever, I could actually feel the small increase from the diablo, didn't with the flashpaq.
Flashcal is nice because you get the screen and you can upgrade it over the internet to a Flashpaq if you later decide that you want tunes. But the one I keep going back to is the simple little Procal.