ExpandSystemMemoryX64=true - invalid description. As i don't have x64 OS and heard about 3.1 gb limit (which is 4 gb), couldn't test myself with VMMap, so thought it's bug in game engine when some buffer pointer used in math, so i did this variable to fix issue by using memory range of 3-4 gigabytes. At same time this greatly reduce memory fragmentation, but effective only for x64 systems as they give 4 gb of virtual address space for 32 bit applications (winxp allow to set 4 gb, but it's very buggy mode and not recommended). I don't know how to describe this to users, but seems this parameter always work for everybody, so let it be true always, some users report that even this enough against their problems.
DisableDriverMemoryManager=false - again wrong, this depends from drivers, os and videocard. Fewer chances to get CTD or low performance if driver is bad and if it have own memory manager. But if driver is good, on the contrary it can give stable work and better performance. Also when set to true, d3d will try to do everything to not show any errors, at cost of performance or long freezes, so it's kind of "do or die" parameter, while set to false it's like "you can't? okay, ctd".
DisablePreloadToVRAM=false - wrong again. Faster loading times because textures and geometry not actually created when game loading, they are creating only when visible in camera. Side effect is stuttering when object not in memory, but very useful when saved game won't load because of too much data in cells (imho simpler just to set lower quality, go to other place to save). Cell transition take longer time only when new cell objects are visible immediately, so not always valid definition.
EnableUnsafeMemoryHacks=false - yes, again. This is for videocards with a lot of video memory, because this mode is if player don't want to have any stuttering, any side effects (except alt+tab issue) or by some reason this set to false not work (reason actually other software). This mode also perfect if user have disbalanced system like 32 bit OS and videocard with 4 gb video memory. This mode don't use dynamic memory reallocation, so no compression, no enbhost.exe. Also it work only when ReduceSystemMemoryUsage=true set.
ReservedMemorySizeMb - this depends too much from 32/64 bit system and vram size. Smaller - less ram usage of the game (fewer CTDs), but bigger in most cases means less stuttering in very heavy areas where many mods used (and ugrid too high). If user have 512 mb of vram, this value 512 is also nice, because entire video memory will be dynamic, it's already small for heavily modded game, so better to not block it by static data. As i understood from posts, lower value also helps to some users with infinite loading screens (perhaps they happen because i'm forcing in cycle to free old memory and try again to allocate for new resources).
VideoMemorySizeMb - this is very unique for each system. What you wrote is correct, but not for users like Goliatron. Other d3d9 mods, web browsers, many other software want to use vram too and bad drivers add more headache. Almost all systems have vram available greater than physical vram, but some users reporting driver errors when vram is completely filled up with data (above i wrote why). If system is clean and only game is running, this value can be very huge, for example 16384 should work for rig with gf660 2 gb + 16 gb ram. But! If you have 6144 for 4 gb of ram and 2 gb vram, don't even think about running something else while playing, because there is a huge chance that non local video memory (ram actually) size will reduce because of other application and you will get very low performance or CTD.
Don't know if i need to spawn another one or two enbhost processes if one will not be enough (it now can handle only about 6 gb ram compressed); something with other mods not work, seems those which modify geometry; additional thread will help to reduce stuttering when cells loading; more experiments with statistics of texture usage per frame also may decrease stuttering when not enough vram, but a lot of textures; small textures on the distance may greatly increase performance to allow run even with 256 mb vram. A lot of work, but at least i may not afraid to forget how everything work and make graphic changes (which i don't remember now, ha-ha).
If you have freezes with values above vram size, get another drivers and close all software, run the game only, no mods like sweetfx. If you can't, then set a bit less than vram size.
athlon ii x3 2.9hgz, 3gb ram, geforce 650 ti 2gb, winxp x86