Note: This is a copypasta of a reply I did to a topic.
I think the VRAM thing is more complicated than "[Game] uses X amount of VRAM, therefore, you need more than X amount of VRAM these days" for performance. I've been reading on the interwebs from people that games will request more VRAM than they actually need and they may never use it, much like how apps may overshoot how much memory they need (yes this is actually a thing: https://blogs.msdn.microsoft.com/oldnewthing/20091002-00/?p=16513). Though in a lot of cases where I've seen VRAM usage, the game tends to use the same amount regardless of VRAM. e.g., a game uses around 4.5GB of VRAM regardless if there's 6GB, 8GB, or 16GB.
So what about the case where a game uses roughly the same amount of VRAM regardless and there isn't enough? I'm not convinced there's a huge issue here. So here's an example (from https://www.techspot.com/article/1600-far-cry-5-benchmarks/ )
Given that Far Cry 5 uses around 3GB of VRAM at 1080p, this may not be much of an interesting result to look at but for the record:
Now the 1440p and 4K benchmarks should be more interesting. Clearly Far Cry 5 will use more VRAM than the GTX 1060 3GB has
Yet strangely enough, performance, even the min FPS results, aren't tanking hard and is remaining in line with the expected performance delta from the GTX 1060 6GB. In fact, even the GT 1030 is only seeing a linear drop-off in performance despite having 2GB of VRAM (1440p is basically 2x 1080p, and 2160p is 4x 1080p)
And for all the research I'm willing to do, I came across a PcPer article interviewing one of NVIDIA's VPs of engineering, with the most interesting bit being:
If a game has allocated 3GB of graphics memory it might be using only 500MB on a regular basis with much of the rest only there for periodic, on-demand use. Things like compressed textures that are not as time sensitive as other material require much less bandwidth and can be moved around to other memory locations with less performance penalty. Not all allocated graphics memory is the same and innevitably there are large sections of this storage that is reserved but rarely used at any given point in time.
tl;dr, VRAM usage may not actually be indicative of any actual requirement of what's needed.