I thought I may need to post some explanation about the DisplayProductID file that was provided above.
Without the file:
This display natively exposes an EDID to the video card that contains the resolution 3840x2160 in 60Hz and declares it as its native resolution. It also exposes the resolutions 4096x2160 in 50 and 60Hz as secondary resolutions.
MacOS X honors this when it starts, and shows 3840 as the native resolution. You can show the secondary resolution by using the option key in the System Preferences.
Plus, all scaled modes that you can get will be derived from thie 3840. Meaning that all modes will be 16:9 and not 17:9
I repeat: without the file, for MacOS X, this monitor has a native resolution of 3840x2160, and a secondary resolution of 4096.
Who is faulty from LG or Apple, I don't know.
In some cases, I also found that the EDID is not read correctly from the monitor, and the 4096 resolution is not there at all. Plugging out and back in the monitor sometimes forces the reading again and make the 4096 show.
With the file:
When you install this file, MacOS X will not use the EDID from the monitor, but the one in the file.
This modified EDID only removes the declaration of the 3840x2160 as native. This implies that the 4096 resolution is now seen as the native one.
MacOS X then recognizes that this monitor is 17:9 (and still can show 3840 because this one is secondary).
As such, all scaled resolutions will now be derivated from 4096 and are 17:9, and no more 16:9
Moreover, as the EDID is now in the file, it doesn't have to be read by MacOS X from the monitor, so no read error occurs.
As for 50 vs 60Hz: in the file both resolutions are declared, and both can be shown. If one is shown on your system and the other not, it's only because the driver didn't enable it. Probably the 60Hz resolution bandwidth is out of the specs of the driver. That CANNOT be corrected with this file.