The thread is here:
New/Better Wheel Option for Spec Z . He's making an 18x10 square set for the SpecZ crowd, and the offsets look good for us too on paper.
FWIW, my current square setup (that works and doesn't rub, with the APRacing BBK and the car lowered an inch or two on my coilovers) is Forgestar F-14 18x10 +34 all around, and using a 10mm spacer (the type that's just a plate with holes in it, from Z1) in the rear so they come out a little closer to the fender back there, with 275/35R18 rubber on them (RS3). I got the offset info from travisjb + Mike who have both run a similar setup at some point in the past. The upside of same-offset all around on the wheels themselves is you can rotate wheels between all 4 corners and flip tires on the wheels, etc. Less waste on un-rotate-able tires.
As I mentioned in Brian's thread, I think the offsets he's putting on his SpecZ setup will end up ~5mm further out than mine, so it's in the ballpark and will work, although who knows yet on brake fitment and whether you'd want a little spacer in the rear for looks.