Strider,
You are correct about the greater availability of brass and factory ammo for a Super. However, there is no factory .38 Super that will make IPSC major. Factory 9X23 will (is Winchester still loading this??).
I am not sure if the greater size of the rim on a .38 super is an advantage. This causes rim stack, which is a primary reason why such rimless cartridges as .38 Supercomp and .38 TJ were developed.
I do agree with the advice on the AFTEC extractor. This was developed by Rusty Kidd, the gunsmith that built my open gun. And i have never seen a more reliable race gun, ever.