There must be some software these machines have in common other than windows... So all these machines have a clean windows install (from MSDN-SHA1 verified iso!), and what happens afterwards? Some registry hack you do on all of them? All running the same AV? All connected to the same NAS where some virus lives in? Some weird radiation or magnetic fields (working on your laptop while inside a microwave oven?)? Try to do a clean install, then install 1 program at a time with enough time between them to be sure the scrambling can come up if it want's to. You really should try to isolate the problem this way. Going to bed now, maybe the night brings an explanation. Oh, and can you provide us with a photo of the scrambling?
Your blaming win7 for memory leaks? Perhaps you should wait for win7 to mature before using it . What are the the laptops? Do they have updated bios for win7 support? You've been very vague. Are they really old???
The machines have an age difference of up to 5 yrs. This isn't an install media issue, as it has happened when I did a Win8 install from a clean ISO, unless a virus somehow managed to infect the ISO during the DVD burning process... It's also happened to me initially with Vista, which is why I've never went back to that OS again. Anyways, these kernel 6.x OSes lag more than XP. Apps not only load faster in XP, but I can get more fps in games too. I essentially gonna stick with XP for a long time yet and screen scrambling isn't the only gripe I have with them "modern" OSes...
Get yourself a good ISO and run Malwarebytes.Do Proper install and things,hopefully,will work fine for you.Anyway thank God you made up your mind.