From my perspective, if the OP is correct that it takes 5-10 seconds to zoom to 1:1 when 1:1 previews already exist, then there is something not right on the system. Yes, the current hardware isn't the fastest, but it's only marginally slower than my Windows desktop, so it shouldn't make that much difference (it takes around 1 second to zoom to 1:1 with previews pre-built on my system, using 5D3 files). Advocating the free upgrade to LR5.7 is fair enough, but advocating an upgrade to LR6 and Windows 10 is not something that I'd personally do as the starting point, I'd want to do some investigation of the current problem first (hence the questions that I asked in my first post). Such an upgrade, by itself, isn't likely to see the 1:1 zoom time get down from 5-10 seconds to where it should be. That might only happen if the current software/hardware install is so messed up that the upgrade sorts the mess out....though on that basis a repair/reinstall of Win7 would also likely fix things.
In terms of Win7 vs Win10 performance, I have been running a series of timing tests, using the same set of images, on every new release of Lightroom since LR3. Over that period I have additionally added my OSX system to the test cases, and have upgraded my Windows 7 system to Windows 10 (though in the latter case the hardware remained the same). As a consequence, I have some historical timing comparisons between the two versions of Windows, and almost without exception there is very little difference....some tests are marginally faster using WIn10, some are marginally slower. The key word being "marginally". Of course, these tests don't cover all LR functions, only some of those that I can objectively measure (building 1:1 previews, and exports). Subjectively, LR performs pretty much the same using Win10 as it did using Win7, the only obvious difference is that startup time under Win10 is a little longer than under WIn7....I suspect there's something different going on with the power management of my internal hard drives, which is probably configurable but I haven't got round to looking into that yet.