GPU Overclocking not changing benchmark results

I'm trying to overclock my MSI GTX 670 Power Edition with Afterburner but with little success.

The main problems are:

(1) Heaven Benchmark results remains the same no matter what I clock to.
(2) What was stable at one point is no longer stable after I restart my computer


Before restarting my computer, the following is what I was able to clock to and the result from Heaven. Now I can't even overclock to +100 core clock no matter the voltage. However, if I reinstall Afterburner, it will work again until I restart. However, at no point do the clock speeds actually change my benchmark results. I had similar issues with Kombustor. Sometimes Kombustor would even tell me that the clock is down to 700mhz even though the clock offset was set to +100 or +200.



Partial system specs:
Mobo: Asrock Z77 Pro 4
CPU: 3570k at stock clocks
Power Supply: Raidmax RX-730SS
GPU: MSI GTX 670 Power Edition

*Stock*
20.3-45.9-118.6

*Voltage and power limit max adjust*
23.0-46.0-118.0

*Core clock +100, all voltage, power limit*
-Failed

*Core clock +100, only power limit*
19.9-45.9-118.6

*Core clock +150, only power limit*
-Failed

*Core clock +150, power limit, +20mV*
21.2-45.9-118.6


*Core clock +200, power limit, +20mV*
-Failed

*Core clock +200, power limit, +50mV*
19.6-45.9-119.0

*Core clock +250, power limit, +50mV*
-Failed

*Core clock +250, power limit, +75mV*
16.2-45.9-119.7

*Core clock +300, power limit, +75mV*
-Failed

*Core clock +300, power limit, +100mV*
-22.1-45.8-119.4

*Core clock +350, power limit, +100mV*
-Screen turned green, had to restart

*Core clock +325, power limit, +100mV*
-Computer froze with visual artifacts, had to restart