any rtm version that has none of these patches introduced??..... I know subsequent patches may have added to the base rtm edition...
I would venture to guess that any version of Windows 10 that was released prior to January 2106 and that has absolutely zero security updates installed would not be patched for Meltdown/Spectre in any way. Any build released after January 2016 is either partially or fully patched. Is this a theoretical question or are you actually considering doing it?
if you running them under virtual or sandboxed or under linux or macos then you can use plain vanilla iso's i guess as long as those third party stuff fully patched and updated
of course you take that chance but you just reboot to run again like embedded and thin clients that clean up cache every reboot if done properly like sandboxed but yes nothing ever safe when you have scoundrel gov/hackers in every country doing cyber/hardware/software hacking these days and worse
The entry creation date for Spectre 1, Bounds Check Bypass CVE-2017-5753 is 01/02/2017. The date where it became public was later, though. (January 2018). Official date of discovery is 6/2017 (wiki). There was no patch in the year 2017 yet. If you want an unpatched OS I suggest to use LTSB2016 By discovery of Spectre a new era of vulnerability has been born. Side channel attacks and data leaks from cache or buffers. Since it is based on CPU design (and branch prediction) there never will be a complete patch and always new ways that will be discovered and later tried to be patched. Security has been given up to gain CPU speed and patching leads to performance loss and regains security at best. The Coffee Lake refresh to prevent Meltdown even makes the I9 more vulnerable to Fallout compared to older hardware. Since there are many different hardware / OS combinations out there actually each one would need an own patch plan to get properly patched, but that is hardly possible.
on which Intel cpus? are you being paranoid or something? my old machines have not suffered any "performance hits" or drops with the recent win10 patches installed. as for the OP, he should use either ltsb 2015 or ltsb 2016 (hey my doctor's pc at a local hospital runs ltsb 2015 - I had an appointment with him earlier this September)
sure new machines decent but depends on workloads so you like me don't use workloads that take performance hits yet or never will if we don't use certain software or usage - even my 12 yr old laptops on core 2 duo not any slower other than browsers more bloated and more memory usage depending on number of tabs open paranoid i am not but the news is always out on security forums of breaches daily, weekly and so on but i keep going on as long as my machines patched and third party always getting upgraded as well as bios and firmware and drivers updated; and it is all cpu's for now as far as i know until i see different for gen 9 and gen 10 as it was the design architecture so intel is probably bandaiding 9 and 10th gen but that will cause a hit somewhere else or hackers will find other vulnerabilities; don't fret just keep updating as we cannot ever be 100 percent safe in life humans are flawed and create flawed stuff -- i just report the news i don't create it
and speaking of web browsers, the meltdown & spectre patches are also implemented on the browser level and not just the windows os level (oh yes, they're included in modern Firefox & Google Chrome versions) and some of my machines use AMD cpus instead of Intel - so I'm not too worried about any performance hits or slowdowns since I barely notice them (like only small slowdowns)