1 - Startup time is affected by all the bloat
2 - Trial for slow/crappy AV, affects IO and CPU usage (more than other anti-virus)
3 - OEM "tools" that make it "easier" to use the computer, consuming a non trivial amount of CPU to check for updates, show several tray icons because of course you need a special utility to switch from builtin screen to external monitor even though the builtin one works better and by the way do you want to sign up to our special partner offers?
I suggest you smash a finger with a hammer, when I did that it hurt but of course it's only anecdotal evidence
I have used countless installs of Windows, through MSDN, retail, Technet, and through vendors like Dell. I happen to avoid being a suggestible simpleton so I don't simply adopt the sophistry that is so common. Sorry if this offends you into hilarious insults.
It's not a matter of benchmark, it's about computing 101.