@Jason,
I remember on BMW
press releases and on the drawings in the catalogues, the E90 M3 was listed as wider than the E92 M3. Based on your two threads, this one and the
F82 M4 vs E92 M3, i think there is an error in the specs since the F82 vs E92 thread lists the E92 M3 width as 1821mm (vs E90 1816mm).
There's some inconsistency there. Official specs say E92 M3 (L/W/H)mm as (4615/1804/1424)mm and E90 M3 as 4580/1817/1447mm.