Thanks for the detailed response. It seems I didn't really check the compatibility properly, lol. I own this piece of RAM:
http://www.newegg.com/Product/Product.aspx?Item=N82E16820231589the parameters are the same as you listed though, it just looks different...
Interestingly, when I powered up my PC an hour ago, everything worked fine. BIOS went really fast (when this "bug" occurs, it takes several seconds for it to happen) and even the HUB worked fine. what I did:
BIOS:
1. disabling fast boot (it booted faster than with fast boot, anyway, lol)
2. enabling full memory test on boot
3. disabling xHCI
4. disabling the power saving feature that powers down USB when the PC is in state 5 (shutdown but with PDU turned on).
5. lowering CPU overclock from 4.4 GHz to 4.3 Ghz (i5-4690k with custom cooling).
Well, at least it booted up fine, but not sure whether it will work once I turn down the PDU for the night.
Perhaps that's the solution as well, keeping the PDU on
Certainly seems a better idea to me than RMA'ing the mobo and being computerless for 2 weeks.
I will also enable xtreme memory profile, if the problem returns. Currently it's disabled (as by default).
my CPU is i5-4690k, running at 4.3 Ghz atm with all voltage settings on auto. That's not exactly by the Overclocker's book, as I am supposed to tweak the voltage, but it kinda worked fine without it so I just went with the flow. Since it doesn't even hit 60 degrees on 4,4 Ghz at full load, I'm thinking about 4,6 - 4,7 Ghz being possible. But first, I have to sort out this cold start bug of course.
EDIT: well.good news, after like 0,5h with PDU off, the system booted off normally without the RAM issues. But the USB hub still doesn't work untill replugged. Damnit.