The Witcher 3 - 8GB of System RAM
We've color-coded the VRAM amounts in our the graphs in case you'd like a quick AMD vs. Nvidia analysis, but remember, this is not an AMD vs. Nvidia test. Yes, as we'll see, there are some minor differences that can be drawn between how the two brands of GPUs use VRAM, but our focus is on RAM usage here.
And right away, we see what appears to be an increase in RAM usage with VRAM size, but look a bit more closely, and you'll realize that the Nvidia cards skew those results a bit, as our R9 390X 8GB card actually required less RAM than the R9 290 4GB, while the GTX 980 Ti 6GB used less than the GTX 980 4GB. But yes, the 2GB card used the least, so if you want to view this as potential evidence in favor of running more RAM when using more VRAM, feel free! Whatever the reason for the difference seen here, it has nothing to do with the VRAM in use: all five of our cards are using right around 1400MB of VRAM, which is a testament to both the quality of the game code given its visual fidelity, as well as its optimization on both AMD and Nvidia platforms.
The Witcher 3 - 16GB of System RAM
Again, VRAM usage is amazingly consistent across our test cards, averaging around 1450MB, which is interestingly a bit higher than when less system RAM was used. We'll chalk that up to chance. As for the RAM usage, we again see Nvidia cards using more, but this time the 980 Ti 6GB uses quite a bit more than the 980 4GB. Somewhat perplexing is the fact that the three AMD cards now all use around the same amount of RAM. And in fact more system RAM begets more system RAM usage. Go figure!
Battlefield - 8GB of System Ram
When Battlefield 4 came out in October 2013, it was one of the very first game to actively use more than 2GB of VRAM. Many enthusiasts viewed it as the death knell for 2GB cards, but as it turned out, BF4 was aggressively caching data, and could run perfectly well on cards with just 2GB of VRAM. That being said, if you throw more VRAM at the game, it will use it, as we see that our cards with the largest amount of VRAM also use the most. We also see that unlike The Witcher 3, the Nvidia cards are using more VRAM in this game.
And what about the RAM-VRAM connection? Well, the only thing we see here is that our 2GB card again uses a bit less, while the other cards are all equivalent based on GPU manufacturer.
Battlefield - 16GB of System Ram
With more system RAM, we again see more RAM being allocated, and this is likely just a Windows caching mechanism, similar to how the game engine intelligently uses more VRAM when available. And this time, our 2GB card uses the second-highest amount of system RAM. Overall, we'd say there's no pattern of more VRAM requiring more RAM.