My OP clarifies the exact nature of efficiencies, which is quite narrow, and not over broad - efficiencies related to performance and stability.
It also tries to clarify my usage and perspective, in order to guide what kinds of efficiencies would matter, even more narrowly. Some examples I gavce were -
- New things "below the hood" that significantly enhance disk access, file shariong access, desktop software compositing, and memory handling for larger processes, for example, especially when used with VMs and with office + browser packages.
- There might be a significant API change that means a whole area of issues no longer causes problems it once did, or a whole new subsystem.
- I also state that I'm not a developer, but an end-user, so matters that a developer would need to know for coding purposes, aren't important to me unless they will impact me as an end-user.
The question asked is, "what specific OS changes are noteworthy between an up to date Windows 8.1 install, and an up to date Windows 10 install, that people have noticed or which are publicly known".
A full list obviously can't be given, but the idea that a list could be open ended or only contain highlights relevant to the OP's apparent needs, hasn't ever stopped a good summary of factual relevant key points from being a valid answer. So the idea that the question could be "opinion based" because an opinion is needed which facts to curate, isn't really a problem. Mainly because the question is tightly defined and has guiding examples of relevance. Pick what seems useful and applicable, like any other question.
The underlying matter seems well defined, tight, and factual - if I were a microsoft technical specialist, what would the main differences since latest WIn 8.1 be, that a user might gain from, if they move to WIn 10? Answer - factual list of highlighted points. There is a new version of SMB. Explorer can handle long paths properly. Security enhancements such as controlled folder access. WDDM 2.x may significantly reduce memory demands for intense compositing. Win 10 updates are notoriously stablity-rocking, but LTSB doesnt have that problem. All factual points relevant to the question's narrow limits. None subjective beyond answerers deciding "is this likely to be relevant to the OP" which is usual and not what the close means.
Can this question be reopened?