An Nvidia 6800 is more than adequate.
I suspect it is EITHER your video/motherboard chipset drivers.
OR
It's a memory issue.
Vue eats memory like there is no tomorrow.

More than likely, it's the later.
Check the windows "task manager"(right click taskbar/task manager) while you're working. Select "Processes" tab. Click "mem usage" to sort running processes & see what program/s are eating your memory.
It's also a good idea to add the "VM Size" column to your task manager - click "view/select columns" & tick the "Virtual memory size" box.
You'll notice Vue eats a hell of a lot of "VM"(leaks!?).

Increasing the amount of physical memory (RAM) AND Virtual memory will increase your VUE performance.

So..Update your drivers & increase your "virtual memory" and see how that goes...let us know what happens?

Cheers.

It's a shame stupidity isn't painful.