I just got a Seiki 4k monitor.

I am trying to get it to run at full resolution but so far no luck. It defaults to 1080i 60hz.

This review says it works by adding a mode with xrandr but he is using a different video card then me:

I am using a Radeon HD 7870 with the fglrx-updates fglrx-amdcccle-updates on 13.04.

I followed the advice in the review and added a new mode with xrandr but when I try to change the output I get:

xrandr: Configure crtc 0 failed

When I try to switch using amdcccle I get:

The current settings cannot be applied. Possible issues may include:
- Display(s) cannot be enabled.
- Setting(s) cannot be applied due to insufficient video memory.

The video card definitely supports 4k resolutions and I know it's possible to get it working on linux. I just can't figure out how to get it to work for me.

Any help would be appreciated.