A few days ago, I upgraded my good and tried desktop PC from i3-3220 with HD 2500 to i7-3770 with HD 4000. While I expected they would be similar, since these are CPUs from the same Ivi Bridge generation, but the new graphics started straining my eyes and nervous system immediately. The whole picture and the text feel less stable. Colors have changed and are not as "warm" as before. The picture is brighter and causes strain in the forefront, the eyeballs, and maybe even in my heart. Thus, my good old CCFL Philips display has suddenly become bad. Its PWM never bothered me, but now it does at the brightness of about 70%.
I tried a couple of different drivers and Ditherig. It's all the same.
Could there be any other causes, like changing from legacy BIOS to UEFI, etc.? I also upgraded RAM and SSD.
It's a pity that I'll have to get back to the old CPU with significantly less power — I'm changing the CPU back tomorrow. Hopefully, the picture is back to normal then.
Now I know by experience that if it works, don't touch it.