One thing I noticed, is that you should raise your lerp value. Wouldn't have a massive effect on your game, but it may be helpful.
What else did you have running in the background? Windows Live messenger? Skype? etc. Keep in mind that programs like these often run in the task bar (bottom right be default), even after you "close" them.
Did you have any browsers (including steam browser) open?
As always, check the condition of your computer. Shut it down. Clean it. Restart it. Try it again.
Make sure that enough cooler air is making it into the case. Don't have your computer sitting in sunlight, or have it right against a wall/desk.
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