Need Help on Overclocking A8-3870K

Here is my current clock speeds with the corresponding BIOS settings

A8-3870K @ 3.0 GHz (undervolted @ 1.25 Vcore)
HD 6550D @ 757 MHz (stock is 600 MHz)
ASRock A75 Pro4-M (BIOS v1.50)
G. Skill Ripjaws X 4GBx2 DDR3 1866

CPU NB Frequency Multiplier: 900 MHz
CPU NB/GFX Voltage: 1.200 V
GFX Engine Clock: 757 MHz
DRAM Frequency: DDR3 1866
DRAM voltage: 1.500 V
APU PCI-E Voltage VDDP: 1.208 V (min: 1.208 V / max: 1.800 V)
APU DRAM PHY Voltage DDR: 1.200 V (min: 1.200 V / max: 1.400 V)
CPU Load Line Calibration: Auto
SB Voltage: Auto

It is stable in gaming, video encoding, and watching HD movies

My problem is when I try to set the GFX Engine Clock (HD 6550D) to 800 MHz or higher while retaining all other BIOS settings, my PC crashes when playing HD movies. But it is stable in gaming

I tried increasing the CPU NB/GFX Voltage to 1.325 V but the problem still persists. I returned CPU NB/GFX Voltage to 1.200 V then increased APU PCI-E Voltage VDDP to ~1.300 V but my PC still crashes when playing HD movies

I don't know what to do anymore. I really want to make 800 MHz stable and hit higher speeds on HD 6550D. I have seen lots of review sites being able to reach 800 MHz to 900 MHz. The review sites didn't go into specifics, they just indicated in their reviews that they set the IGP voltage to ~1.3 V.

I'm confused with my board's BIOS settings. I don't know which one is for the "IGP voltage"