So exceeding the 4GB on a single Fury is OK, but crossfire with the same settings is a problem? Odd. Maybe whatever magic they use to get around the 4GB cap doesn't work in crossfire? That'd be kind of absurd though as that's where it is needed most.
I recently fried a 980TI so I'm weighing up various options, but I don't have an unlimited budget. Nanos seem to be a good price at the moment so I could get 2 or 3 of those (over time), but I'd be locked in for a while and I don't want to hobble myself.
I do have a 290 at the moment, so slumming it at 1080p until Polaris comes along isn't out of the question. Hard to guess if wave 1 polaris will be a better deal than Nanos.