Pierce Graphite Columns, do you really get more phosphopeptides than with C-18 Ziptips?

Pierce has been advertising their Graphite spin columns as a more efficient method for desalting and retaining phosphopeptides, but is that really the case?
In this experiment, we took a mixture of phosphopeptides that were enriched by filtered capture and elution (FACE) using the 3G10 antibody as described in this paper from Mathias Mann's group.

The eluted phosphopeptides were split into two equal aliquots.  One aliquot was desalted with the graphite spin columns.  The second was desalted with C-18 ziptips.

The results are pretty clear, although it is interesting that the majority of phosphopeptides pulled out by the C-18 columns were unique to that desalting method.
Our thoughts are to integrate the two techniques, perhaps by desalting the flowthrough from 1 method by the other.  Anything that increases our coverage this easily needs to be jumped on.