There are a lot of things that may be contributing to you getting errors. I personally like to overclock one thing at a time, so I would drop the multi as low as it will go for now and work on getting yourself stable with that FSB frequency.
Is your ram set to factory specs for voltage, and list the northbridge volts as well as fsb termination if you can. At over 400FSB you may need a termination voltage of 1.3-1.35 and the northbridge might need a bump as well. Just raise them slowly and one at a time, then test.
Once you get a stable system at the FSB frequency you want and the ram is running well, move on to overclocking the cpu.
Try the termination to 1.3 or slightly more depending on what your mobo lets you set. And around 1.35 on the NB. You can run 1.4 on the NB as long as you keep it cool, just stay under 1.5. PLL is fine at 1.5.
Like I said, you shouldn't have to worry about the vcore just yet. Lower the multi and work on getting everything else stable first. And again...One setting at a time then test and record results, that way you know what is doing what.
I have a q9550 as well. I agree with all the advice about adjusting one thing at a time. I noticed on your initial post you mentioned setting the voltage to auto regulate. I have a gigabyte P35 series and the default setting had been auto voltage regulation. As I increased my FSB, CPUID was noting that my cpu voltage was over 1.5! I quickly switched the setting to manual. I now have a undervolted (1.15v) Q9550 running stable at 3500 Mhz. I personally liked that blend of power and power/heat savings. I did have to add +.05v to my Northbridge in the end though. It seems like most have oc'd to 3800-4000 or beyond but keep in mind all chips are different.
and My new setting are CPU voltage / Vcore 1.32256
CPU GTL auto
CPU PLL 1.50
FSB termination 1.32
at 450 x 8.5
and the CPU temp is AT 39 to 40c
and at full load about 66 -70
I let prime 95 run 17 iterations and there were no errors this time
I also did research and I found that people that OC there pc from 2 years ago still have no problems and my original setup was for a 1600 MHz FSB which I have been using for about 19 months so I figured if people have been running at 1800 MHz FSB from two years ago and still doing it then I am going to do the same.
MOBO - P5Q Pro Turbo
RAM - 8 gigs Hyper x ram
CPU - Q9550 E0 revision
GPU - ATI 4850
Storage - two 60gb OCZ vertex is RAID 0 - one 500GB WD Black - one 640GB WD black - one 1 WD 320 GB blue - one IDE 160 Gb Hitachi desk star.
OS - Windows 7 64bit Home Pre
thanks for your help O one more thing please give me a good site for tech dibs on the new Intel P68 chipset and LGA 2011 I'm looking for leaked specs.