Even windows chugged badly (in my opinion) when it was new on it! Had to actually boot into windows to disable the secure boot or w/e bullshit on that one (that had me stumped why it wouldn't usb boot). Maybe I'm so used the how fast linux is, but windows felt barely usable, so I think kde would chug at least a little at times. To be fair though, never tried kde. I've gotten so used to xfce, I just roll with it.
Not that one... Yea, my thinkpad was easy for both the drive and the ram (I figured if I have the tools out, upgrade drive and ram for that one while I'm at it...) That one, you need to completely dissemble