I know that makes it even more difficult for me to choose. Should I go with the normal 4GB? Is 256 bus that much of a problem?
I know Maxwell has some secret sauce to make more with less bandwith but 8GB seems excessive to me on such narrow bus.
http://www.hardocp.com/article/2014/09/18/nvidia_maxwell_gpu_geforce_gtx_980_video_card_review/4#.VGIPoflFuUk
4GB on a 256 bus is totally normal on the other hand but I can't tell you how future proof it will be. Unity requires 4gb at 1080p to use the most detailed textures, Shadow of Mordor asks for 5.4gb (at 1080p) if you max the original assets.
VRAM is the wildcard at the moment.