Keep in mind that although IDPA is believed to be about shooting what you carry and tactical, the facts are it was invented, and is owned by, one of the greatest IPSC shooters ever (even before USPSA), and that is Bill Wilson. He and his buddies cooked up the rules way back in 1997, and they are pretty much just opposite of USPSA rules today. Here is a great read.
http://www.frontsightmagazine.org/ar...6featuresm.pdf
If you want to shoot your every carry gun, like in my case a G19 from an IWB holster under a t shirt, I can only do so well as opposed to shooting my G34 from an OWB holster and a photographers vest