@fred aha!  I think enabling lan connections did the trick.  I can't believe I've been dealing with the lag this whole time, and it was something so simple!  I also don't know why that option wouldn't be enabled by default...

@woland, I think I've mentioned this before, but I often encounter a bug when using Mac's VNC.  It's like the client computer doesn't properly recognize the arrangement of the host computer's displays, and when I try to click on anything to edit, the cursor is actually on another screen.  https://discussions.apple.com/...