[MetroMPG]

So a big part of the "it depends" issue would seem to be quantifying what counts as a "smooth" vs. "rough" underbody.

Based on the 5 production examples I linked to above, it would seem those vehicles may fall into the "rough" underbody class, since lowering aided each one.

Also, we can't forget that setting ride height optimally for miniumum drag in production vehicles is probably in competition with practical considerations (e.g. speed bumps), and handling considerations.