the old AS5 was tested across 5 CPUs--
AMD Athlon 2500+ Barton XP
AMD Sempron64 3100+ at 2.3ghz (inconsequential, wasn't even paying attention to these)
an e2180 clocked at 3.4ghz and 1.48v,
an X3 720BE->X4 unlocked, 3.5ghz/2.6ghz 1.47v
a Phenom 2 X4 965BE at 4ghz/2.6ghz 1.44v
FX8310 at 4.3ghz, and it couldn't handle 4.6ghz
this last one was the first with a problem. At 4.3ghz I had no trouble, but 4.6? instantly 66C at 1.443v on In-Place Large FFTs
You know -- I'm looking at this with a little more discernment.
I'm not an AMD builder -- not since I used their replacement for the Intel 8088 processor. Certainly, the power statistic at some particular load test is more important than voltage. My sig-rig and its twin are set to give me a highest-measurable turbo VCORE of ~1.38V.
So I won't concern my thoughts here about what your voltage represents in terms of some "safe range" and an "operable range" above it. I wouldn't know.
But 66C with LFFT test . . . wait-a-minute . . . OK -- with GRID2 in a menu-mode still running, here's a short run of Prime95 LFFT "with AVX" for my cool-running 2700K system:
Room ambient is 78F. This is done with the ACX [aka SuperClock] cooler EVGA 100-FS-C201-KR, and ICD applied improperly, according to the Innovation Cooling web-site and "Application Guide."
CPU pusher fan: Noctua iPPC 3000
Exhaust [CPU-puller] fan: Gentle Typhoon AP-30
Intake fan [side and front]: 2x BitFenix Spectre-Pro 200mm rated 144 CFM
2x 970 GTX gfx cards warm things a bit, so the PCI plates above each card has been removed for an ongoing project and passively directed airflow in the meantime.
The AP-30 is ducted to the rear of the ACX with a ThermalRight blue accordion duct.
I think the peak package temperature showed up at 74C. The Average-of-cores maximum is ~71C, but the prevailing values fluctuate below these extremes over a 3C range. Note the package power maximum pegged at 130W.
So, if you're reporting your peak power accurately, you should be able to do better, but "better" may involve other things besides the cooler specifically and the TIM. In replacing my RAM the other day, I removed the Noctua pusher fan and these thermal statistics increased by about 2C under the dual-fan Fan-Xpert profile. I would have to shift my CPU_FAN "fan-curve" to the left in the graph to regain the 2C.
And after my long sig-twin explanatory babble, the point is simple. Unless your 66C is outside recommended thermal limits for that AMD processor, you're fine, temperature-wise. If the corresponding 1.4+V VCORE is not far above some recommended limit for the processor -- then fine. If it isn't, you choose your own priorities.
But all the temperature reductions in the world with strategies not exotic like phase-change aren't likely to get you extra Mhz unless you raise the voltage. Some other AMD aficionado can pipe in here, but I'm only looking at your thermal wattage, the cooler -- even the paste, and the temperatures compared to what one might like to achieve with my Intel processors.