win7 laptop + win8.1 tablet here. "Classic shell" works perfectly and gets you a nicer interface than even win7. Win 8.1 settings will allow you to disable app updates, app searching and apps altogether, as well as disable all the wiggling "effects" that make the interface impossible to use on a touch tablet. One done you will have a slightly better OS than even win7, which I love.
IMO, 90% of speed improvvements are likely hardware. Board mfrs use a variety of specialilzed chips to speed up the user experience without speeding up the proc speed (which drains the battery). Sometimes there really are things that MSFT can do to make the interface move faster. But in both cases this is independent of CPU speeds.