Asus p5n73-am/phoenix bios/Q8200, OC Problems

I am using the Asus p5n73-am/phoenix bios with an Intel Q8200. I'm having a problem overclocking. I know the MB is a POS,, but I'm broke and want more for free ,,,
The default setting is FSB 1333/MEM 666.7,, 2.326Ghz "2.33" . I can get to around FSB 1440/MEM 750 2.52GHz and it starts to run slow then crash in windows. I don't know what the deal is. I have over clocked this CPU before on other MB/Bios.
Also this Bios has weird voltage settings. I have OC the Q8200 before to 3.0 without touching the voltage. I'm just a rookie when it comes to OC, but I have done it a few time successfully.
Any information you have could help me out,,
Thanks,, Great Site!!

This is different from other bios setting I've seen.
1. the 1.8v dual over voltage control is for what (think ram but unsure)
2. is 1.35 over voltage control ( for cpu right )
3.vcore over voltage control and it has three settings +50,+100 and +150