I upgraded to a GTX3080 10GB (I got it 6 months after I reserved it), I did actually notice some small improvements but that's a graphics card that's way overkill for the sims4. I don't think the game have ever used 100% from it, that sounds extreme. The game is running on an old DirectX9 engine so a newer graphics card is not gonna do much except throw more power at the problem, so performance will improve but not very effectively.
Sims4 can use huge amounts of RAM, especially if you are playing on an older save. In my experience, the following will affect sims4 performance:
- The size and age of your save.
- The amount of objects on your lot and in your neighborhood.
- The amount of played households and their inventory.
- The amount of relationships in your save.
- Using CC that's badly named (don't use special characters).