I just finished upgrading to W10 on an overclocked g3258. Went fine in one pass without messing with the BIOS. I suppose the fact that I have a z97 mobo helped.
My understanding in that this processor was explicitly designed to be overclockable with the z97 chipset and no other. Mobo manufacturers didn't agree and released tweaked bios'es to unlock the pentium on other chipsets. Maybe Intel decided to get back at them by releasing this stupid microcode for Windows and ... put their foot in their mouth. As a result, any G3258, OC'ed or not would have issues with Windows, unless the chipset was Z97 or the mc-update DLL file was removed. Both Intel and Microsoft are to blame for this. Harshly I reckon.
Before upgrading (which required a registry edit in W8.1 for completion), I renamed the microcode DLL file in ../system32, just in case. I was ready for the next boot to fail and have to tweak the BIOS until I could rename again in W10. Did not happen : the update took about 30 minutes clocked at 4.3.
One could feel some anger towards those geeks working for giant corporations/administrations, crossing the line farther every day. First time I felt really angry about this was 10 years ago about the Sony rootkit. It's getting worse every year and this is a nice illustration of how there doesn't seem to be a way back. Just like I have been boycotting Sony for 10 years, I might consider going AMD, until another competitor finally emerges (like it will aver happen...).
I bought this nice (and expensive) z97 mobo with the idea of purchasing the most expensive broadwell processor later on the road and be OK for a few nice years. Not sure I'll go along with my plan after all.