I have the same problem. Under Load (IntelBurnTest) my q9550 throttles at 52-53 Degrees C. This is fine at stock(2.83Ghz), however when I overclock, it automatically throttles down to 6.0 ratio as temps hit 50+ Degrees.
This might be because the power provided by the motherboard is just not enough for quads when using a four pin power connector.
To get real overclocking, you could try a better board with an EPs 12v (8pin) connection and a suitable power supply.
It is our punishment for having budget boards.