Just to update...
Purchased an R7 370 as my 5850 was not 2/4k compatible. Fair enough. Also got a 4k compatible Display Port to HDMI adapter and have succeeded in getting 1 of the 3 monitors into native 2560x1080 correctly.
The other two DVI to HDMI monitors cannot exceed 1920x1080p even with the updated Radeon drivers supporting custom resolutions. Each time I go to make a custom resolution at 2560x1080 it just throws me an error message saying the resolution isn't supported by the monitor even though it obviously is.
Do you think the DVI-D to HDMI cables I just bought from Amazon are not HDMI 1.4 compatible and thus won't allow the 2560x1080 resolution?
Should I attempt these (http://www.amazon.com/gp/product/B00MCSMX4Y?psc=1&redirect=true&ref_=ox_sc_act_title_1&smid=A33H9NEZM9VEGY ) with the HDMI cables included with the monitors?
How are people physically hooking up their 4K eyefinity setups?
One more update. Just switched a 2nd monitor to 2560x1080 but using HDMI > HDMI rather than the DVI-D port.
Unfortunately the last DVI-D port still won't accept/display above 1920x1080 and i'm starting to suspect it's a limitation of the DVI-D (despite everywhere saying it can display 2560x1600).
Looks like I wasted a 170.00 bucks on a card with not enough 2k/4k outputs. I guess i need to go buy another card with 2x Mini DP ports and an HDMI so I can get 3 4k compatible output streams.
Well solved the issue. There is some type of bug/hardware issue with the R7 displaying above 1920x1080 via DVI-D. I could get two monitors at 2k resolution using an active DP to HDMI adapter and the HDMI to HDMI cable but the 3rd going via DVI-D (not DVI-I) and using the correct DVI-D cables would never output above 1080p. So how did I solve this?
I bought an Nvidia GTX950... plugged it in and made NO changes to the cables I was running and voila all 3 monitors running 2k resolution without any issues. On this setup i'm still using one active DP>HDMI adapter, one HDMI to HDMI cable, and one DVI-D adapter to HDMI cable as I was using before but for some reason Nvidia supports this correctly. Not sure if this is a software or hardware issue but AMD support said the R7 would support it and that clearly is not the case. Was an Eyefinity fan boy for 6 years. Never again. Wasted 3 weeks and a couple hundred bucks trying to solve this and it turns out I wasn't the problem in the scenario.