My Spec:
Phenom II X2 555BE (stock hsf <<== will change to CM hyper 212+ next month)
kingston DDR1333 ram (will get another stick next month)
Asus M4A785TD-V Evo (Bios ver: 2005)
MSI X1300 Pro 256 PCI-E (got it free from friend, no playing games so tis gc enough already)
160GB hitachi sata hdd (old hdd)
Coolermaster 750W GX series PSU
Old CoolerMaster mid tower casing
Win 7 Ultimate 64bit

Successfully unlock to 4 cores
bios setting:
ACC mode enable
unleashing Mode auto
CnQ disable
C1E disable
voltage auto (but it'll automatically went up to 1.3750V-1.39V sometime, so i manually set the voltage to 1.3125V)
multiplier set to 17x (O/C to 3400Mhz, stable with Prime95 running for 12hours)
tried set multiplier higher than 17x but running Prime95 for half hour the system auto reboot.

room temp 24C, cpu temp with full load 45C-47C
room without air con just ceiling fan, cpu temp with full load 56C-58C

ur cpu voltage set to auto? maybe u can try lower the voltage to 1.3V. it can help the cpu produce less heat.... i've try set to 1.3V run Prime95 12hours stable. and the cpu voltage won't hit more than 1.3V. if 1.3v not stable try add a litter until it's stable on full load.

here is mine ...

then u gotta verify the prob cause by ur 64bit win7 or it's hardware issue(eg cpu, ram, or mainboard setting). I'm using 64bit win7 also. so far no bsod if just unlock 4core and everything set to auto. then i set the voltage to 1.3V and O/C to 3.4Ghz@4core start windows no problem, run Prime more than 10hours no bsod, hang or auto restart prob.
i've try set the voltage to 1.28V but not stable, sometime cannot enter windows it'll auto restart, even successfully enter to windows if run Prime for 1-2 hours it'll auto restart also.
so i guess my cpu is best with 1.3V.

i've the same cpu batch like yours, and same motherboard. Have no problem to unlocked 4core. Is your power supply enough power for that? and did u disable the CnQ & C1E in the bios ?