Using the maximum in-game quality settings at 4K saw VRAM usage climb to just over 6GB when using the R9 390X. Despite the massive VRAM requirements the R9 390X was just 2fps faster than the R9 290X, which is almost surprising. As we have suspected, the R9 390X simply doesn't have enough horsepower to deal with that much data, so while it can store it, this doesn't help the GPU get anything done faster.
For an average of 30fps the R9 290X is required while the GTX 970 just fell short, though the difference between the two shouldn't be noticeable. The same goes for the R9 390X and GTX 980 as both are just capable to delivering playable performance. Ideally those playing at 4K will want the GTX 980 Ti at their disposal, and once the SLI bugs are worked out two cards will deliver some pretty nice results.