@MrTonySM Your post is making realizing something indeed!
Yesterday someone was enquiring about why is it Task Manager was reporting his GPU was “allocating” more RAM that what’s available onboard. And I’ve answered this is normal because the API (DX11 for example) is allocating RAM to store buffer data when you pass it to, then is keeping some buffer data in RAM even after streaming the data to VRAM, in case the buffer is discarded and need to be re-uploaded later to the video card. This is normal and expected.
And here is the connection to your post!
The 3090 ships with 24GB VRAM and if you fill it with buffer data or textures, you’ll certainly also duplicate a large amount of the VRAM buffers in RAM, and there you are: with 32GB RAM you probably really don’t have enough room to fit both the buffer data copy in RAM and the game working set!
Conclusion: everyone with a 3090 might really benefit from 64GB and this might even be the minimum recommended amount of RAM to use with a 3090.