The culprit? Virtual PC 2007
Along with the updates, it appears that Virtual PC 2007 x64 ALSO causing the jittering in FFXI and 0 FPS inside of EQ2–even if VPC isn’t running. I’m assuming it uses some sort of hook driver against the primary video card (I really need to research this), but uninstalling VPC solved the issue.
Serious grumble here… serious grumble.