Hi again, everyone.
This is certainly proving to be a challenge for all of us, however, I want to reiterate the findings from my last post.
My "New" iPad is now successfully syncing all 6,435 .jpg photos through iTunes (10.6.0.40). The .jpg photos vary in size from 200KB to over 4MB and many exceed the 1920x1080 dimensions mentioned above.
My four other Apple devices, including several iPod's and the original iPad, continue to syn perfectly with iTunes on Windows 7 and never exhibited the syncing problem that appeared on the New iPad. That means this is definitely specific to the New iPad.
I did not have to remove or move the original photo directory on my Windows 7-64bit PC or its 20 sub-directories that hold the 6,435 photos..
I did not have to laboriously sync 10 photos at a time to the New iPad.
What I did have to delete were all photos from the New iPad (several times over several hours).
I did have to delete the iPod Photo Cache directory several times over the same several hours of troubleshooting.
Finally, the one step that appeared to make everything work was to uninstall the retina-optimized version of iPhoto, which I installed before I first tried to sync photos to the New iPad.
Once iPhoto was uninstalled, I did proceed cautiously by only syncing several photo directories at a time to check the results, but after a few minutes, all 6435 photos were perfectly synced - nothing lost and nothing corrupted.
Since I am using the same version of iTunes, the same photo directories on Win7 and the same New iPad, the only thing that made everything right was the removal of the retina-optimized version of iPhoto.
Now, that isn't to say that with all of the frantic deleting of photos multiple times and deleting the iPod Photo Cache directory mutliple times, that somewhere along the way something wasn't affected "under the covers" on the New iPad.
In my case the problem is resolved and I've added photos to the source photo directories and re-sync'd several times since.
I have since re-installed iPhoto and everything still syncs fine.