Did you do any tests since?
The release notes for these new drivers mention fixing "visual corruption". Since that's what I was seeing, I now think that perhaps there's nothing wrong with the iGPU on my CPU, that it is in fact a driver bug. There were no crashes or BSODs with 4300, just some minor image corruption in Waterfox.
And you should run Windows 10. Windows 7 isn't fully supported.
Says who? Win7 64-bit is a supported OS, until 2020. And the drivers specifically mention Win7.
Maybe MS may not be handing out WHQL certifications for Win7 drivers anymore, or something like that, but that does NOT mean that Win7 isn't supported.
Edit: Heck, plenty of businesses only JUST switched from XP to 7. And you think that Intel is going to simply just abandon all of those corporate users, that use Intel CPUs and IGPs? LOL.
Edit: Or worse, corporate purchasing managers explicitly choosing 4th gen Core systems (Haswell) over 6th gen Core (Skylake), specifically just to stay "Fully Supported" by Intel for Windows 7. Do you really think Intel wants that, to keep businesses from not even looking at their most current hardware offerings?