This came out of the discussion of 4731797, which was for windows.  
We need analogous work for Unix.  

>>>>Are there settings on
>>>>Solaris/Linux, analogous to SM_CXDRAG and SM_CYDRAG, that
>>>>we should take into account?
>>>
>>>I don't know of any such setting on X.  Perhaps Valeriy knows of one.
>>
>>Under GNOME there's Net/DndDragThreshold XSETTINGS setting (8 by
>>default) - that, judging by its name, is pertinent.
>>
>>Motif text components seems to be controlled with XmNselectThreshold
>>property (5 by default).
>>
>>Motif List widget has the threshold hardcoded (at 3).
>>
>>IOW, the good thing about standards is that there's so many of them to
>>choose from ;).
>>
>>I'd check Gtk2 and how it uses Net/DndDragThreshold.  Since the
>>XSETTINGS code is now in the workspace we can use it to read and track
>>the properties we need.