Stuttering might be a better term.  For the initial small window, I did not see much difference between 2.7 and 3.4. At full screen on a 25xx x 14xx screen, both stuttered. If the 2.7 looked better, it is because it redrew slower.  If I zipped the mouse fast enough, the border temorarily disappeared instead of being repeatedly redrawn. But full-screen empty panes were not as bad as the quarter-screen demo with each pane full. From Ned's comments, Windows simply does not handle this operation as well as Mac.

The left.pack and right.pack statements are not needed as left and right are 'add'ed to the PanedWindow.

The easiest way to expose more text is to enlarge the Window with the text frame heavily weighted. This would allow people with big screen to grab the right edge, pull, and leave the window with both text and canvas fully exposed. With ttk (but apparently not tk), the panes can be weighted.
  paned.add(left, weight=10)
  paned.add(right, weight=1)
(To 'compensate', showhandle seems to have been deleted for ttk.)

The same can also be done with grid. The advantage of using the paned window is to give more flexibility to people with small screens, who cannot view both text and canvas simultaneously. However, I am not sure about the acceptibility of switching to ttk, especially before 3.5. Perhaps I should ask on pydev.