I think one should really understand what their needs are in a GPS. Water resistant, vibration resistant, sufficient memory (or pre-loaded maps), auto-routing, XM, NEXRAD, ability to generated PC-designed routes, and the list goes on.
You have many riders here in Georgia that run a GPS...you might better serve your purpose and seek them out to see what they are using, how it's mounted, and why each rider choose the unit they have. Some of the rallies and rides are good places to meet them.
Good luck!