My current PC is a Q9400 on a P5K running at ~3.4GHz and i'm fairly confident overclocking that and what everything does.
My missus has decided she wanted a PC to play games on after cooking her laptop trying to play Planetside2. We initially looked at getting a laptop more suited to playing games and quickly realised such laptops were overpriced and provided much less performance compared to much cheaper desktop components.
So i got her another "normal" laptop, and set about building a desktop for her from some bits i had lying around.
In the end all i had to buy was a motherboard, i had a Pentium G6950, 8GB 1333MHZ Ram and a GT520 knocking around as well as a case and some drives, however i found it REALLY difficult to find a motherboard which would take the LGA1156 chip. Most retaillers seem to have stopped stocking them (and yet finding LGA775 boards still seems possible...) so I ended up with an ASRock H55M-LE bought from ebay in a "refurbished" state, and i think this may well be the cause of my issues.
I read various guides and decided the starting point would be to try and find the BClk/QPI limit, much the same way as i'd search for the FSB limit on my P5K. I pegged the multiplier at 9, set the ram speed as low as it would go, and gave the IMC some more voltage (1.25v) and tried 166MHz.
No POST, just a black screen and a few power cycles later the motherboard booted on default settings saying overclock had failed.
I messed around a bit and found it would boot at 150, so i worked my way up from there and got to 165mhz. Upto 165 its perfectly fine, boots perfectly and will even run at full multiplier (21x) to give a stable 3.46ghz overclock with only a slight +0.05v bump to the VCore. Clearly the chip has much more to give, but the BClk just wont go any higher.
What i cant figure out is why 165 is rock stable at almost default voltages, but 166 doesnt even POST. I tried a few different higher values, including 167, 168, 170, 171, 173, 180 and 200, just incase there was some sort of hole with the same result. I've tried turning the IMC voltage up to 1.35v, upping the VCore by +0.15v, dropping the QPI multiplier right down to 12, but none of it makes any difference.
Is this typical of what you would expect on a LGA1156 platform? That it would just hit a wall and refuse to even POST if you try to go any higher? Is it likely to be an issue with my CPU or the motherboard? These G6950's seem to clock well typically, and i was expecting to get 4GHz from it.