Do each update one at a time. A restore point should be created after each. Save the .net framework one for last. This will tell you which is causing the slow down. Once the computer slows down after a particular update, do a system restore, then hide that update.
With automatic updating turned on, you don't get the option of only doing updates one at a time. They are downloaded and installed automatically. As the OP says, when he restarted, they all installed.
I've never seen a situation where every available update can't be installed at once (unless explicitly set that way by Microsoft). On XP, Vista, and 7, I've always done every possible update in one go, and never had an issue with it.
This slowdown is related to a recent update, and the computer will sort itself out after a bit. I've already dealt with it on three computers, and it will fix itself.