I have had close to similiar problems around 260 fsb. Heres what i run.
Biostar TA785G3 785N 710S
AData DDR3-1600 99924 1.65v 2x2gb
Now what im set at
2610mhz NB +.15v
2610mhz HT stock volt
1333/3.33x mem. multi. =1740mhz@10101028 1.7v
You should be looking at up voltage at this point on the cpu and nb. If youd rather you can keep the nb near 2ghz and should need to touch its voltage. In my BIOS if you limit the NB to X8 it does the same for the HT basically you can set the NB higer than the HT but not the HT higher than NB. Anyways keep your memory, NB, and HT, as close to stock for now to find the max FSB. Really simple math is only involved.
DDR800 = FSBx2
1333 = FSBx3.33
1600 = FSBx4
So for your memory you want to be at 260x2.66=1383mhz close enough to stock if you havent done this your running at 260x3.33=1731mhz which would be pushing your memory real hard and most likely unstable. Second thing you want to do is set NB and HT multi's to 260x8=2080mhz close enough. Now after that try and boot if no go try upping the cpu voltage .05v then .1v if still no success then i think your running into the same problem Im having with memory reference clock(FSB) being to high for RAM see below. Hope you understand this remember everythings speed is based off of the FSB and then multiplied you try to keep all other components near stock by adjusting multi's.
This is rock solid prime95 blend test 24/7 stable temps no higher than 48c on ACPI 45c on cores. Now the odd thing is I reboot over and over with no post when set to 264 no matter what changes I make and BIOS roles back clock speed due to to many cold restarts. 263 is prime95 small ftps stable (doesnt test ram) but fails blend test that stresses memory. The really odd thing is that I can run just this one particular stick of ram and boot at up to 270. The other stick wont. Im going to order some DDR2000 sticks and see if i cant hit 3.9ghz+ like Ive seen some do with DDR2 it seems that lower end DDR3 cant handle the higher FSB frequencys.
Well good luck and keep me posted. Shared knowledge is power and progress.
More Advanced Micro Devices than Intel