Windows 7 works well, Win 10 works just as well. I don't care for the tiled menus of Win 8-10 so I use
Start10 ($4.99) on all my Win 10 PC's.
The biggest bang for the buck upgrade you can make to an old PC is changing out the HD for an SSD. SSD's are now cheap (120g Adata on Amazon for $37) and make bootup and all operations faster...more so than even additional memory.
I just made my grandkids a Win 10 PC from a Dell Latitude 620...probably 10 years old now. 1.67g Core 2 Duo processor and 2 gig of memory I think. Anyway, first installed Win 7 then 10 on it and it's 160g HD...was horribly slow. Threw the $37 Adata SSD into it and it runs great....better than any $300 PC you can get...I know I bought 2 and returned them as they did not perform as well as this old PC.
I say go for Win 10 and update your HD to SSD.
Also, Microsoft updates are mostly for cyber vulnerabilities and are usually released for good reason...I would not turn off my updates. I think the recent slowdown of the update server is because everyone is racing to update to Win 10 before the deadline in 5 days.
Just my 2 cents.
