(Catching up and reviewing the bidding here...)
1 - First of all, let's get your card formally recognized to see if that helps, sometimes it does with cards in that series, or at least to see if we can rule this out. It can't hurt, anyway. You would think that there is enough information in that huge dxdiag to work with, but afraid I need one more log file. If you could, please send me by PM a copy/paste of the first 40 lines or so of the DeviceConfig.log file that would be in your TS user game folder in Documents. You can stop when it gets to the long lists of game options, we don't need to see those.
2 - On the texture memory override fix, the game can only use 800 MB of video memory. We usually advise 1024 MB on the fix, so just a bit more than that, some have gone a little higher, but I am not really sure what could happen with a setting as high as you have used even though your card is much more capable. I'll include the way it's usually done in the sgr file edits once I get the DeviceConfig info.
3a - I am also suspecting that your long running ongoing game is toast and that you may need a Plan B to Get My Sims The Heck Outta Here into new worlds if we can't move this forward. But let's not jump to that conclusion just yet.
3b - You mentioned that your saved game (or is that your entire Saves folder?) is "only" 677 MB. The critical thing here now that the days of too small C drives, etc. are left behind, is what is the size in MBs of your currently being played (or attempted to be played) homeworld's nhd file within one of those individual saves?
4 - Obviously you have plenty of RAM to work with now. According to Task Manager, how much RAM is the game itself using before it crashes or Error12s, if you can manage to see it before you suddenly end up looking at your desktop with no game running instead? The actual RAM usage on just TS3.exe or TS3w.exe, not the percentages, which might require a hidden column to be revealed in Processes on the Task Manager. I think you might be hitting or getting too close to the game's ~3.7 GB RAM usage limit. That one cannot be overcome because now matter what kind of hardware we run the game on, it's still a 32-bit application. The best we can do is see how much gameplay we can get out it while keeping things (far) below the RAM danger zone and the upper limit.
The sudden and almost immediate drop to almost 0 on what the game calls available "virtual memory" is concerning, but I suspect it's the ongoing save trying to load up that's doing that and what we are seeing in the crash log is really a symptom and not the problem itself. Maybe we can work through that as per the above.
