It sounds like you've hit the limit on either the motherboards ability to push power to the chip or in fact the chip is just not going to make it that far.
Vdroop is where a processor pulls power at a certain rate and the motherboards ability to stabilize the voltage isn't good enough to keep consistent voltages. Even if you are pushing say 1.4v at idle it may drop clear to 1.35v at full load. This is what LLC is for. If your motherboard doesn't have it; that does kind of suck as overclocking with touchy voltage amounts gets really difficult. If the motherboard just can't keep up then it may be the motherboard being the issue. I've actually had a couple motherboards that just couldn't handle the pressure of large wattage processors. Once you start overclocking them the VRM's just get pounded and don't do a good job keeping a stable voltage through the processor. This is where motherboard quality comes into play a LOT.
As for the CPU, each chip is different. While one 8210 chip might do 4Ghz at 1.35v, another chip may need 1.4v just to boot at 4Ghz. So it's one of the two but from what I see; it's probably the chip being nasty.
I'm not real familiar with that chip and haven't used that motherboard at all. But see where the "Safe" limit is for that CPU and if you can run the voltage and clock it; try it. From what I see with a quick google search cheti pretty much nails it. 1.45v for around 4.5Ghz. So you're looking at really getting that voltage up on the chip just to get it near 4.5Ghz. Now remember, just because someone else hit 4.5Ghz at 1.45v doesn't mean your chip will.