Everything working nicely now:
http://tinkertry.com/enjoy-windows-8...ernal-monitors
using Lenovo's variant of the DisplayLink Windows 8 drivers (latest DisplayLink drivers work too)
Woo hoo, victory at last! Strange that putting the NVIDIA 1000M into Discreet Mode, coupled with turning off VT-d in the BIOS, was most of the secret sauce.
Guess I'll just have to let go of the iPad 4th screen option I had shown at the bottom of this article:
http://tinkertry.com/mydesk
So glad such DisplayLink products exist at all, finally, 2560x1440 bliss, with 3 external monitors, on a laptop. Awesome!