The reason mobile 3080s have more vram is that it's slower and cheaper memory. It's GDDR6 and only runs through a 256bit bus whereas a 12gb desktop card runs much faster (GDDR6X) and has a 384bit bus.
The extra 4gb won't be making as big of a difference as the increased bandwidth (~913GB/s vs ~448GB/s) on a desktop card, particularly since the game is being measured to use less than 12gb of allocated vram (allocated != used) in most areas. There are also people with 3090 and 3090tis reporting stutters. Would guess 4090 too but haven't seen anyone talking about that and i haven't tried the game again yet since the first version of the demo. the problem likely lies elsewhere.
I have seen people talk about general performance on a 4090, and when I see things like people saying frames drop below 100 into the 60-80 range frequently even on that, it tells me something is very, very wrong.
You can compare it to games like God of War which are more demanding in terms of raster performance yet they perform better overall. If digital foundry hasn't already made a video about this one I hope they do.
XI Wiki



