i5 4670k voltage
i5 4670k voltage
I don't recall what others managed to achieve with that CPU. It's been a while. Check out some old reviews to see what voltage they used. Of course, each CPU is unique and your outcomes will differ, but you'll get a general sense of what to expect. You can gradually increase the voltage until it stops booting or becomes unstable, then lower it again. Or if adding more voltage doesn't boost performance further, reduce it. Don't need to push it to 1.3 if 1.28 gives stable MHz output.
What kind of motherboard are you looking for? CPU temperatures can exceed 1.3v if the cooling isn't sufficient. The earlier Haswell chips, such as the 4670k, usually get quite hot around that level, but refreshing with Haswell refresh chips like the 4690k can help a bit. From what I've gathered, achieving 4.4ghz is a solid overclock for that chip, though stable at 1.3v might be challenging unless you're lucky with the hardware.