The IPDA rules are pretty simple when you're dealing with unaltered guns. They're really just broken down by caliber/action type/modifications.
There are some oddities along the way. You can shoot your G35 in SSP with its extended mag release and slide release. But if you put either of those parts on your G23, you're in ESP. If you leave your G23 totally stock except for a stainless guide-rod, you're in ESP.
Your Caspian will be in ESP since it's a .40.
Shorty .40 - SSP
.40 Limited - ESP
Sig 228 - SSP
HK .45 - CDP
Taurus - SSP
G20 - CDP
Witness 10mm - CDP (I think)
If you shoot more than 2 divisions, you'll be changing holsters an awful lot.