Do you mean it runs slower on Win 10 than on Win 7? My patch introduces extra performance hit on high resolutions, because it scales UI in software in single thread. Flexible UI is less demanding, because less of the screen is covered by UI.
As in compared to the performance that would be exhibited on hardware the game was written against at the time. This is primarily due to fundamental video hardware architectural changes with drastically different performance characteristics that the MM6..8 engine/old D3D API is designed for, exacerbated by the emulation layer that has to emulate correct (API-level) behaviour on this hardware (not to mention the game is just poorly written in general)
Profiling shows, as expected, frequent stalls due to CPU/GPU synchronization resulting in up to a whole frame worth of delay (halving the frame-rate, minimally). GPU work isn't fed efficiently at all; small batches due to constant state changes; GPU spends most of it's time either idle or doing non-useful work tasks, even driver rename pools for resources are exhausted occasionally due to the pathological modify-read-write pattern, etc.
Rendering the UI in software is of negligible performance concern and is a primitive matter of being memory-bandwidth bound (or, should be), however it's the sort of workload that video hardware is designed for and would benefit it.
tldr; average frame rate is about 22fps on modern commodity hardware during scenes of typical complexity.
Where? I only saw the stack trace/error log the game usually generates.
I was sure it did, because I have the savegames (the ones I played on this computer on windows span august-november 2015), but when I tried reinstalling and applying the latest grayface patch mm8.exe complained that "some" (unspecified) files were missing, while using mm8setup.exe or running mm8.exe as admin worked.
Right so you reinstalled the game, installed GrayFace's patch, encountered what is likely a permissions issue the game reported misleadingly as "missing", then ran it elevated and it worked? That sounds about right, although I'm a bit confused as it seems you're suggesting otherwise.
Regarding the present issue (with the Merge version) -- have you followed the steps listed?
Well, the virtual store UAC employs to "protect" users does the exact opposite of that - it breaks old games.
I was pretty sure that Program Files was among the special folders for Win7 UAC.
And I see you are starting to understand why I hate UAC and Microsoft in general.
Again, not related to UAC -- see my previous response.
File-system virtualization (and registry virtualization) which is what you're referring are nothing more than mechanisms to aid in compatibility for legacy (pre-Vista) software which frequently assumed they'd be run with full administrative privileges.
Only software that does some pretty esoteric things (e.g, the redirection is implemented in UM, thus it's possible to inadvertently circumvent it) will be affected.