I had been using windows 8 consumer preview and recently did a clean install of the retail version. One of my regular speed tests is to run skyward sword's title screen at 4xIR in D11, since it's one of the slowest parts of the game.
Before the install i was getting 20fps, 40vps, now with the final windows 8 i'm getting 23fps, 46vps. I had a mountain of updates to get through and even after a dozen of them it hasn't changed. Not 100% relevant to your situation, but updates haven't hurt in my experience.
Are you aware of what specific updates you downloaded? If you could track down which one caused the speed drop then you could see what it was for and figure out how it impacted on your system.
Before the install i was getting 20fps, 40vps, now with the final windows 8 i'm getting 23fps, 46vps. I had a mountain of updates to get through and even after a dozen of them it hasn't changed. Not 100% relevant to your situation, but updates haven't hurt in my experience.
Are you aware of what specific updates you downloaded? If you could track down which one caused the speed drop then you could see what it was for and figure out how it impacted on your system.