I am running an i7-4770 (non-k, turbos to 3.9)/r9 290 4gb/16gb ddr3 1886mhz/SSD and recently did a clean install of windows 10 (including killing as much of the bloat as I could). I just ran a fresh KSP install with only KCT, Magicore, ClickthroughBlocker, Toolbar Controller and Module Manager. No lag or stutter in the editor or anywhere else.
I figure I'll post my Gamadata directory with some added notes in case it's useful here. If theres a better way to do it, please let me know. Everything is updated to its latest available (I check daily) and manually installed (no CKAN). I have updated any Agent.cfgs to get rid of any title errors in the log.
I also have the x_input.dll crash when changing scenes that some others have encountered. This leads me to believe that it is indeed a system specific issue, or just a result of the single thread bottleneck (I get 25-27% total CPU usage) which is why I finally gave up spending all of my time troubleshooting instead of playing.