I wish I knew more about the SQ series, the more I read about them the less like the previous S series they seem to be.
My EC focussed down to inches.
My Bronnie buds say (about the SQ and filling a frame with face) that the 135 and 180 give closer focussing for head portraits, or you can add an extension tube to that 150 of about 15-20mm, but you might have to compensate for exposure, or close-up diopter.
This is something that irritates me a bit about my Mamiya 6, doesn't focus close enough, but then its not designed to take that type of shot being a rangefinder.
I was used to using the EC, and reading up a little, apparently its the closest focussing of any 6x6 slr, nothing else can touch it, not a Hassy, Rollei, Kowa, nothing....:shrug:
I gotta say, it was fairly stretched out at the far focussing end, like the first 6 feet was all within a half turn, then it didn't seem to do an awful lot for the rest (full turn after the half turn).