This is an intriguing idea, but is this something that would change at some point? I'm looking for reasons a computer would be slower after several years, not right off the bat.
I've seen computers get slow because of installing too things that demand a device driver or service be running.
iTunes is a big one because it installs Bonjour, which on Windows, has been successful in slowing down certain operations (such as inserting a 30 second pause in every shut down or sleep/hibernate the PC does).
You could skim services.msc to see if there's anything in there that shouldn't be.
Cleaning out %temp% of course...
Temporarily disable A/V to see if that fixes it (rarely seen that work but you never know).