i've tested 2 matrox triple head (DP) with the 2 thunderbolt output on only 1 mbp retina.
It works :o), but i've only :
2 projector on the first matrox triple head,
and 1 projector + 1 screen on the scond matrox triple head
2x 2x 1024x768,
cable : display port to vga
tested on mbp retina 10.8, max 6.
could someone test it if have more ?: 6 video-projector for example