I had the same idea but after reading the rules for the ammo skip system, to get the best effect you definitely need a revolver. The ammo skip system with a clip just ejects the ammo you don't want until it gets to the good stuff. It does mean you can load the first half with stick'n'shock and the rest with ex-ex, but you won't be able to change from one to the other without a revolver.
The one I went with was the warhawk with an external smartgun system, increased cylinder (to increase ammo to

, ammo skip system, improved range finder, firing selection change (small) to SA and then if I remember correctly I didn't have many slots left, if any.
As for Dredd, he would definitely have skinlink, biometric reader, custom look, personalised grip, advanced safety system with an upgrade for shocking unauthorised users, a bunch of camera upgrades and DEFINITELY a voice activation.
Load it up with your favourite ammo, but remember the warhawk can't use ex-ex.