Thanks for the kind comments, but ... The plot thickens.
The previous solution was working, but was not fully the recommended settings for the monitor.
There are the pixel dimensions or resolution (2560 x 1080), and I got this to work, and it fixed the stretched problem. But then there is “refresh rate” or frequency. The recommended setting for this monitor is 2560 x 1080 @
60 Hz, but the best I could achieve with SwitchResX was 2560 x 1080 @
50 Hz. I’m not sure of the performance implications of this discrepancy, and maybe 50 Hz would be close enough, but I began to wonder…
These LG widescreen monitors are the leading brand. Why does SwitchResX not offer this setting? Why should I have to do all this custom configuring? So I wrote to Stephane, the author, asking if it were possible he could add 2560 x 1080 @ 60 Hz as a standard setting.
He wrote back that there was an FAQ about this very issue that explains “why this is not possible on most Macs and what you can do to get your monitor working on these Macs.”
Basically, every monitor has something called an EDID (Extended Display Identification Data) that describes its capabilites and preferred settings to the graphics card of the computer. If the graphics card is capable of supporting that exact setting, you get plug-and-play. If not, you get a generic setting stretched to fit.
SwitchResX has the ability to read the EDID of the monitor and export it as a text file (I discovered by chance) and consulting that text file, I determined that although the display is rated as 60 Hz, it actually means 59.978 Hz. So I thought by entering 60 Hz, I was actually exceeding the maximum setting. Therefore, I entered 59.978 Hz in the appropriate field in SwitchResX (and matched all of the other exact settings from the EDID document), but I still couldn’t get it to take! Why?
I wrote Stephane again and learned that “pixel clock” is essentially the bandwidth (screen size in pixels + refresh rate) and that on most older Macs there is a limitation of 165 MHz pixel clock, which is why I could get 2560 x 1080 @ 50 Hz, maybe even 51 or 52 Hz, but not all the way to 60.
Then after more googling, I discovered this brilliant link:
https://github.com/Floris497/mac-pixel-clock-patch-V2
This guy, “Floris497” in the Netherlands has created a “pixel clock patch” script that updates and extends the capabilities of various Graphics cards in older Macs.
(The hardest part was finding the link for the script itself! It was not at all easy to spot on the page and many many people miss it. That took some time, and some googling and reading various forum messages back and forth between Floris and other users, where he responds in limited English. He kept saying “you need to download the zip file”. Zip file? WHAT zip file? It was like some dancing, monitor-nerd, Wu Li master who can only respond in cryptic zen hints:
“Hahahah, Grasshopper, you must seek the zip file and all shall be revealed.”
FiNALLY, I found the zip file, ran the script, and it required downloading and installing all sorts of developer tools and such from Apple (this whole time in way over my head, with terminal commands and "disabling SIP", and such
), but in the end, IT ALL WORKED!
I now have updated graphics capable of natively supporting my monitor settings, and I no longer even need the SwitchResX shareware utility.
And it did seem to improve my display performance somewhat. The reds were a bit oversaturated under 50Hz, and things seem a little crisper now under 60 Hz. It also got rid of the LG monitor message that would pop up each time I restarted saying I was not using the recommended settings.
I have learned a lot from this, way more than I wanted. Pretty much the antithesis of “plug-and-play,” and I’m half ready to return this monitor and get something else. But I’ve come so far…. This was like an Indiana Jones quest, following the treasure map that had to be deciphered from the original Mayan hieroglypics, fighting snakes and booby traps, finding the secret entrance to the hidden temple, to eventually revealing the treasure. But I found it! I’m off to collapse in the fetal position for a couple of days…
Mike Halloran are you reading this? 
