After previous rumors that AMD's Radeon R9 390X could have only 4GB of High Bandwidth Memory due to design limitations, FUD Zilla now claims we may see a 8GB version in early summer:
In order to put 8GB on the card you need eight 8Gbit chips (1GB per chip) with 1024GB/s bandwidth. This does sound like a beast and this is what an ultra-high-end card from AMD should look like. The downside is that the yield of 8GB cards is probably lower than with 4GB of cards and that they are more expensive to produce. The benefits are clear, as you get more bandwidth for super high settings at 4K and UHD (3840x2160), or 5K and beyond.
The decision to go for an 8GB Fiji rather than the planned 4GB version was in part attributed by Nvidia’s Titan X 12GB card announcement. This is just the first part of the story. One of the main reason is that the card is expected to perform so well in 4K gaming, that the 4GB frame buffer could impose a serious limitation.