If you have to get a video card now, the only thing I can tell you is one with 2GB, or more, video RAM *might* be needed to be able to run with all the bells and whistles. It *might* need to be in the upper 1/3 of the NVidia/AMD lineup, if not higher as well, to run with everything enabled.
Please note that could be way off by the time we release and anyone taking this as gospel is just begging to make an error in the video card purchase.
You want a guarantee? Buy the fastest video card available, with 4GB (or more) video RAM. I feel comfortable saying it will run with all the bells and whistle enabled, but I could still be wrong.