Thanks all.
It's actually more things like the auto-updating which is driving me bananas with W10, so running Openshell/Start10 etc won't do enough (ime) to make a difference.
Running w10 under vmware is an option, but I slightly worry that I'm ending up with a tech-heavy solution and I wanted simple - I can do a fresh w7 install okay, and that was really my favoured route.
I actually got back 60GB yesterday on a disk clean by removing old Windows update files and compressing the OS - given I can't just put w7 on this, then I think that I'll stick with w10.