BTW I have been running win 10 preview since January.It's faster and more stable than win 8.1 so far.Win 8 and 8.1 is much faster than 7 ever was.
Win 8 was a bit wonky with the app crap,no start menu and it used [WDDM] Windows Display Driver Model 1.1 and that was designed to be used with Win 7 ONLY but they did have a 1.2 Update.1.1 caused ALOT of driver incompatibility problems in win 8.
Win 7 was great at the time but required more Memory usage.
Win 8.1 has great memory management and driver compatibility but still has a slightly Wonky Start menu.
Win 10 has a fully customizable start menu and so far it does everything I need it to.
This discussion makes me consider trying the beta of 10 but the lowly old laptop I have for it gets a bit cranky. Maybe it will be an improvement. In many ways I see upgrading all Windoze users for free is much cheaper in the long run for M$ as it reduces the versions to support.