I would agree that Marc's lens idea would be ideal. However, talking about real world lenses (and referencing yeatzee's example above) the F 28mm 2.8 *is* indeed different from the other 28mms, and not exactly "blah" in my eyes. \\
And yes, optical formula is exactly what I'm referring to. The same thing that differentiates between the M 40 2.8 and DA 40 2.8, which, IMHO, are quite different.
The bokeh of my 28mm was not wonderful, but not terrible, either. The samples I've seen from the F 28mm are a clear improvement, and at that focal length, I don't havu much trouble with "only" f2.8, as long as wide open is usable.
DOF control is good enough for me:
Although, to be honest, I used my 28mm mostly for snapshottery (and preferred a large DOF, because this was one sharp lens).