Yup, I uninstalled the ATI drivers as well; although checking back at Device Manager, the default integrated GPU was listed under Display Adapters (before installing the new drivers)
Then when I reinstalled the newest nvidia driver for my GPU (266.58), the same hanging/freezing/lagging issue came up, along with the "266.58 has stopped responding and successfully recovered" issue (Event ID 4101: Display driver nvlddmkm stopped responding and has successfully recovered.)
I will be trying to see if a previous version works.
If I can't find any solutions at all I'm going to blow my brains out.