Greetings guys  

I recently purchased this  motherboard and so far i had been running my system on  default settings flawlessly for about a month.Here are the specs :
CPU : i5 2300
GFX : Nvidia GTX 550Ti
Ram : Corsair  XMS  1600 , 9-9-924 1 ,65  V CMX4GX3M2A1600C9 
HDD's : 1x TB WD, 1x250 Seagate
PSU : Coolermaster eXtreme power plus 500
1 DVD and 2 case fan connected.
All was well, until i inserted the extra  4 GB's of memory, another pair of the ones  mentioned above, to the total of 8GB. After upgrading, my system would crash in windows with all 4 sticks inserted.What i've done so far
1)Left everything at default settings, left the mem running at 1333 Mhz and 1.50V .
2) Used the  XMS profile in bios, which upped the speed to 1600 MHz , voltage to 1.65 and Vtt to 1.15
 Neither worked 

. Tried the same after upgrading the bios to F4 (altho i have seen F5 mentioned, i saw no link on the official website), tried both of the above, didnt work.
Then i went into the bios,  used the default settings of 1333Mhz and 9-9-24,  but upped the voltage to 1.66  and Vtt to 1.20 (bios would now show dram voltage to be about 1,65) , was stable for a couple of days, but eventually had some minor glitches in game and finally ,another blue screen.
Have tried the old memory in  both memory slot pairs, so it's not an  issue of faulty dimm slots. Admittedly tho, i have only ran memtest for 2 passes on the new  sticks, so i guess i should do more tests to exclude faulty memory .
Apart from that, what other settings can i tweak if it's only a voltage issue and the motherboard just needs a little boost to cope with all dimm slots being full ?. Regarding QPI/VTT, is there any limit i should definitely avoid breaking ? apart from that and Dram voltage, what else can i chance in bios to try and stabilise my rig ?
Also, would you think that maybe the PSU is having issues providing sufficient power ?
Sorry about the long topic, just tried to describe the situation as clearly as possible 

  Thank you in advance for your help