Well, swapping PSUs would have been my first suggestion. And ensuring you were not overclocking (stock BIOS settings) would have been another.
Heat is always suspect so you might try opening the side panel and blasting a desk fan in there.
As for your house current, IMO, ALL computers should be on a
good UPS with AVR (automatic voltage regulation). A surge and spike protector is little more than a fancy and expensive extension cord as they do absolutely nothing for low voltage anomalies like sags (opposite of surges) and dips/dropouts (opposite of spikes) or long duration high voltage events (except cutting power). Backup power during a full power outage is only the icing on the cake. The AVR is the bread and butter. But like PSUs, there are cheap and there are good UPS. A better UPS has, for one thing, a much faster cut-over time and a "cleaner" output voltage.
Also, every household should have a
AC Outlet Tester. I recommend one with a GFCI (ground fault circuit interrupt) indicator as it can be used to test bathroom and kitchen outlets too. These testers can be found for your type and voltage outlet, foreign or domestic, at most home improvement stores, or even the electrical department at Walmart.
Note you say you have the BIOS set to the default settings but then you say the i5 3570k is at 4.3GHz. The default speed of the 3570k, as seen
here, is 3.4GHz, 3.8GHz in turbo mode. Did you mean 3.4GHz?
This could be a RAM problem too. You can test RAM using one of the following programs. Both require you to create and boot to a bootable floppy disk or CD to run the diagnostics. Allow the diagnostics to run for several passes or even overnight. You should have
no reported errors.
Note, however, that software based RAM diagnostic tools are good, but not conclusive. So you might try running with just a single RAM module to see if it fails. Repeat process with remaining modules, hopefully identifying the bad stick through a process of elimination.
I also suggest you pull your extra drives leaving just the boot drive, and any other extra attached devices and see what happens.
How old is this system? It could be a bad motherboard.