What are your RAM stock settings? I would underclock the ram (not timings) at least that takes it out of the OC equaiton.
On the UD3P, the ram divider is called System Memory Multiplier. I think 2.0 is as low as it goes (so it would be 2.0xFSB to give you your ram speed). Then I would up the vcore bit by bit until you are stable. You probably won't need to touch PLL, VTT or MCH voltages until you are using a higher FSB (or CPU Host Frequency). Once you have your OC stable you can up your ram speed using these multipliers to be as close to your stock settings as possible. There are only so many memory multipliers available but in the end you may end up running your ram a little bit under or over spec (up to you). Still, better to have faster CPU then ram
Of course keep an eye on temperatures as you up vcore. Have fun!