Underclocking RAM problem

[Duncan NZ]

Okay, first my setup:
Gigabyte P965-DS3P
E6600 (currently @ 2520MHz 9x280)
2GB DDR2-800 RAM in dual-channelmode, 1GB is transcend and one is Apacer
XFX 8600GT

So its not flash ram or anything, which is why I don't want to run it (much) above 400MHz (Effectively 800MHz), although it is currently running at 420Mhz.

So, in order to take my processor further I want keep the ram at 400 or below and the motherboard only allows adjustment of the FSB to RAM ratio, which it automatically sets it to 3.0 i.e. at 266MHz FSB the RAM effectively runs at 800MHz (as DDR2-800 should).

Problem is as soon as I change the multiplier to 2.5 the computer fails to boot, and seeing as I'm aiming to get a nice overclock of about 333MHz FSB (Giving 9x333= 3.0GHz), this is the multiplier I really want as 333x2.5= 800, the rated speed of the RAM.

Incidentally, I tried changing the multiplier to 2.0 which works under the stock FSB of 266MHz (so effectively running as DDR2-533), but fails to boot as soon as I try to overclock it, so I can't even try a 9x333=3.0GHz with what would effectively DDR2-667 RAM

Any ideas on how I can get my 2.5x multiplier to work, without buying new parts?

 

[Pro_AJ]

What is your ram Voltages? try increasing them a bit

 

[Duncan NZ]

Well, I've put them at 1.9v (Up from 1.8), but cause I'm trying to underclock, I really don't think it should be nessecary. At the moment I'm just trying to have the RAM run at lower speeds before I push the CPU up.

I can't see why it refuses to run at 700Mhz (280*2.5) or even 667 (266*2.5), when it runs fine at 800.