Another Windows 10 Update Causing Problems (windowsreport.com)
New submitter sexconker writes: The recently-released cumulative update for Windows 10 (KB3140743) is reportedly causing problems. Symptoms include crashes, BSODs, and the inability to boot, even in safe mode. The Windows 10 subreddit has many threads detailing the inability to boot. The only fix seems to be booting to a recovery ISO, uninstalling the update / rolling back, and hoping you don't get hit again. W10Privacy 2 claims to be able to (among other things) give Windows 10 users control over the automatic updates.
Windows 10 is fast on everything I've put it on, and that is a lot more than three machines.
Without physically being there, it is almost impossible to help you.
Side note: The "oldest" machine I've installed Windows 10 on is a Core2Quad Q6600 2.4GHz machine that is now 9 years old, it has 4GB of DDR2 RAM and a 80GB Intel G2 SSD, and it is amazingly fast for its age. Oh sure it isn't nearly as fast as modern machines, but if you're checking e-mail, facebook, or playing light games, it frankly is pretty snappy.
Windows 10 is the best release since 7, and before that, XP. Loving it every day, no regrets...