Can't use 2560x1440@55Hz over HDMI under linux (win7 works)

Hi,

Until some days ago I used 2 of these korean 2560x1440 displays on the dvi ports of my 660ti.

Because you can never have enough pixel, I ordered a third one which I connected via HDMI (1.4a).

My problem is now, that I can only use the full resolution of this screen under windows. All my tries to replicate the configuration under linux ended with black screens and a system which doesn’t respond any more.

This are the working settings under windows:

I translated this to the following modeline:
Modeline “2560x1440_55R” 221.1088 2560 2608 2640 2720 1440 1443 1448 1478 +hsync -vsync

But like I wrote, all my screens turn black when I try to use this mode.

(I had to disable most/all of the EDID checks before the system accepted this modeline)

My xorg.conf: http://dl.dropbox.com/u/21975173/xorg.conf
My Xorg.0.log: http://dl.dropbox.com/u/21975173/Xorg.0.log
My nvidia-bug-report.log.gz: http://dl.dropbox.com/u/21975173/nvidia-bug-report.log.gz