I haven't found any solid info on what the difference is. Some sites say it has the Bilstein suspension yet these seem to be found in all the non-Spec B's. I know the "fancy racing style pedals" are a Spec B thing for sure.
In terms of the exterior the Spec B's also have a nicer more aggressive front bumper as well and of course the nice 18" rims.
Some say front and rear sway bars and aluminum control arms are a difference. Some others say the Spec B ECU/tune is different and improved over non Spec-B.
If anyone has any solid info or guesses I'd like to know it!