Finally! After years of searching for a way to make my preview window not trip over frames while playing back files with slow zooms, I happened upon the only solution: to move my preview window over to my monitor designated in my Nvidia card as #1.

I have 4 monitors setup in this order from left to right:
3 - 1 - 2 and 4, which is my external preview monitor, sits over #1

Last night, while Skyping, I needed to share my preview window with the other party so I temporarily moved my preview window over from monitor 3 to monitor one and noticed to my amazement and for the first time in my life that I see no stuttering while playing slow zooms. I put this phenomenon through a number of tests and know this now as a fact, What relief! Is there a known technical explanation for this?