Dual channel works with identical pairs or different sticks, provided that the speed and everything matches. It is recommended that you buy them in a pack though, because they're usually tested specifically for dual channel.
Get the E6 stepping, it's better than the E4 stepping. The 3200+ is the Venice core, right? Yeah, that thing will overclock nicely. I have mine overclocked to 2.4ghz with 1.425v running with temperatures at 34*c-35*c at idle or little activity. Keep in mind that my Delta Tri-Blade is running a it's lowest speed too.