Within a month ago, I managed to snag a pair of R9 285s for remarkably cheap, so I have been experimenting with CrossfireX. I was surprised that, with one, I could play Alien: Isolation at 4K with roughly 30FPS. So I was a bit disappointed when crossfire did not properly work. That's always the gamble one takes though - even with Nvidia's aggressive driver release schedule.
Stock clockrates, although they are Gigabyte's offering of the R9 285, which had a fairly aggressive base clock of 973. I played through the game at 1440p, because sometimes the framerates would dip to 12.
40-60 fairly consistently. I noticed dips sometimes, which might have annoyed me if it was a competitive game, but it was perfectly playable. It usually didn't dip down to 40 unless a lot of things started happening at once, like an in-game system failure with alarms and smoke, or sweet-baby-jesus-the-alien-is-after-me-and-i-am-probably-going-to-die.
I don't feel too limited by the 2gb barrier, currently. Metro 2033 Redux (and Last Light) maxes out at 1700-1800 gigabytes. (1080p, max settings sans AA - because SSAA is too damn much.) I think I remember Joker Productions saying that The Witcher 3 operates at around the same maximum at 1080p. Both are great looking games, so I know part of it is the game makers not being asshats with the VRAM. Lichdom Battlemage seemed to gobble up a lot of VRAM, and I did notice some performance hits due to the buffer refreshing during some intense scenes. Nothing quite crippling though. Having a 4gb frame buffer would be nice for a crossfire set-up, but we'll also see what DirectX12 and Vulkan allows us to do with our VRAM.
Anyway, I just got done experimenting with the Fixed Frame Rate feature. It helps reduce frame tearing, but does eliminate it to the extent that Vsync does. Then again, I only tested it in Metro 2033. I was hoping that it would be a nice side-effect.
once you had dvi-d or dp port you could enable it.
I've seen the option on 6970 7970 though enabling dvi-d was pain (could go up to ~1440p - 4k was possible but cost was enormous - 2x7970 at 4k was giving me aprox. of ~15-20fps on crysis3 maxed out) 290x dvi-d enabled by default, vsr was visible and fully functional up to 4k with my 1080p 144Hz 27" panel.
some friends at boinc told me they had this option on 5970 on dp.