I'm also looking at a 4'x2'x2' tank. My original plan was 4 MJ1200s and a 3/4" Sea-Swirl, but after looking at all the efficiency numbers and whatnot, I'm leaning towards a Tunze Stream setup.
I was looking at the 6000's, but I'm deterred by the cost of 2 6000's and a controller (total around $650). Could I go with 3 or 4 6060's instead?