I'm using four 120w 12v panels with two series strings in parallel to give me 24v to the controller (Victron 75/50 mppt controller) via 4ga copper feeds. Im pretty happy with it...
Inverter is a xantrex prosine 1800w via 4/0 cables.
I may just add two more 120w panels to just take up the real estate on the roof that is left, but it will be pretty much plug-n-play whether it just leave it at two strings with 36v, or just do a third string @ 24v.
I think ramping up the voltage from the panels is much more efficient then staying at 12v to the controller.
I do have a brand new morningstar 25a sunsaver duo if anyone is interested.