I've been messing with this for a good few hours now, and I want to know if everything I've done is right, and if there's anything I'm missing.
I have a GTX 980 Ti, obviously not in the game's database. So I followed that guide over on the wiki for getting the game to recognize new cards (basically edited GraphicsCards and GraphicsRules and added in my card's name), and now DeviceConfig says Found 1; Matched 1. So that's all find and dandy. Then I noticed that the DeviceConfig lists my GPU memory as 1, while everything is max. I did some Googling and the only workaround I could find was to go into GraphicsRules again and edit these lines:

seti gpumemLevelUber 4
seti gpumemLevelHigh 3
seti gpumemLevelMedium 2
seti gpumemLevelLow 1

And I changed all the values to 4 so no matter what it thinks my VRAM is uber.

Then I noticed that in DeviceConfig, next to Texture Memory, it said something like 32MB <<OVERRIDE>>. So I looked around and changed these lines:

seti textureMemory 32
setb textureMemorySizeOK false

to

seti textureMemory 1024
# setb textureMemorySizeOK false

Now next to Texture Memory it says 1024MB.

That's all I've done. I can run the game pretty much at a constant 60 FPS, with occasional microstutters but I've come to believe these are just part and parcel of The Sims 3.
Did I do everything right? Anything else I should know? Help would be appreciated. I just got this brand spanking new GPU and I'm scared to death of killing it with Sims.

I think the safest way for your GTX 980 Ti to fit TS3 well is to set it as GTX 580, because the latest it has in its database for high-end video card is GTX 580, I have GTX 680 for my PC set up and the best and safest way to make it work for TS3 is to downgrade it so it runs as GTX 580 not GTX 680. You can edit it in the GraphicCard.sgr file to do that, and yes unfortunately there's no point exploiting the advantage of the video card's performance above GTX 580 for TS3 because we need FPS limiter to protect the video card anyway.

I personally don't run it above 30 FPS just to be safe, because I did fried my GTX 280 back then because at the time I didn't know I need FPS limiter for playing TS3 until I read it here, if you'd like to exploit the advantage of your hardware you might have, I'd suggest it better be the processor, rams and/or with SSD, just don't mess with the video card for TS3.

I play full screen so I just use the ingame option to keep the refresh rate at 60, plus I use Nvidia Vsync which does that as well. My FPS doesn't go over 60, I've checked.
I'm not even really sure how you define microstutters, might not be the right term. It's more just extremely brief FPS drops, usually when my camera is zoomed out and just as I start moving it hands a slight bit. Otherwise, 99% it's smooth sailing. I have 4GHz

Just want to add, if you happened to play with TS3 CAW for creating your own favorite world(s), you also need FPS limiter to run CAW, because CAW without FPS limiter is just the same like running TS3 without FPS limiter, especially when you run TS3 from CAW for testing or editing purpose.

@Fauntleroy
You're actually having trouble with all 3 games - TS2, TS3 and TS4. Although I think TS2 is something completely different? (Is it just the texture memory thing?) Your problem with TS3 and TS4 is similar though with the stuttering.
I wouldn't suggest trying to solve one game's problem in another game's thread, but it might be better if the people trying to help you *know* that your problem isn't limited to just the 1 game. So.. maybe mention it with a link to the other game's thread? (I'm also having this problem with TS4 - wwwlinktothethreadhere, for example.)

Edit: I meant to say, and forgot: the reason I suggest doing this is fixing one game might affect how the other is working for you. I'd hate to see you get one game working perfectly for you.. then one of the other games is worse than it was when you go to play it next. I'm not saying that *will* happen, but it could. Although I have a feeling you just might have to put up with a little bit of stuttering in TS3 and 4 no matter what.

My main problem is the GPUmemory issue. It doesn't recognize my card's memory and sets it at the lowest value, so I have to use the texture memory override fix I mentioned in the first post. I don't know what to set it to though. Is 1024 right? Should it be my full memory, which is 4000 something? (my card is 4gb.) I read somewhere that it could potentially be harmful to use this override though, or that it doesn't actually do anything. I just want to know my game is using more than 32 Mb of GPU memory, but that it's not harming my shiny new card.

Okay, so I followed your instructions in that post with fresh copies of GraphicsCards and GraphicsRules. Should I also do the setting GPUmem values to 4 thing in GraphicsRules that I did before? You didn't mention that in the post you linked. Otherwise, very helpful!
Just to be clear, I don't have dual graphics with an integrated chip. Just the NVIDIA. IDK if that makes a difference to what you were saying.
Also, sorry if this is a stupid question, but I am not too familiar with NVidia Inspector. I have the Guru3D folder on my desktop, and I opened the Inspector exe, opened the TS3W profile, set the frame limiter to 60, applied, then exited. Is that all? Do I need to keep it open?

My main concern is that, by not fully recognizing my card or my memory, the game will over time damage my GPU. Is that likely?

EDIT: I ran my game, and now in the DeviceConfig (without having done the change all values to 4 thing) it lists my GPU memory as 4, texture memory as 1024, and under graphics device info, it lists the name (driver) as NVIDIA GeForce GTX 980 Ti and the name (database) as GeForce GT 650M [found 1 matched 1]
Is this correct? I just replaced the device ID for the first NVIDIA card in the Graphics Cards.sgr with my card's device id. I believe that's what the post you linked told me to do.

Alright, so then I'll assume that I don't need the tweak to the 4 GPUmemory lines in GraphicsRules and that now it's as good as it gets. Finally now I'll actually get to play the damn game. Thank you so much for your help!

Of course, if your "new" computer is 5 years old.....

What are you implying? My "new" computer is about 1 month old as of now. Maybe I'm misunderstanding you but how would I have a 980 if my PC was 5 years old?