RAM - clocks to PC-8000 - no POST with diff divider?

[equilibrium]

I'm having a wierd problem with my P5W DH and my GSkill F2-6400PHU2-2GBHZ.

I've been running it on 6400 speeds for nearly a year, but thought why not try it higher on CAS5.
http://gallery.equk.co.uk/albums/pc/ram-clock.jpg
I can get the ram to PC2-8000 speeds with 2.1v :) (CPU on 2.66Ghz)
(it came up on bootup as PC2-8500 Dual Channel Interleaved tho)

As I'm running on 3.2Ghz, I've had the RAM at 1:1 so it's 6400 speeds on 4-4-4-12.
As soon as I change the divider and timings to PC-8000 and CAS5 (as in image above), it doesn't POST :( even tho at 2.66Ghz and divider 2:3 it works :confused:

I was just wandering if anyone else has had a similar problem :)
I have Hyper Path 3 and DRAM Throttling disabled.

I thought I'd try a BIOS upgrade aswell, but it's not made any difference :(

[genec57]

Try a higher voltage on ram.

[equilibrium]

Try a higher voltage on ram.
I just gave 2.15 and 2.2 a go, but no difference :(

Was ok on 2.1v with the cpu at 2.66Ghz

[monza1412]

When passing the 300 fsb barrier with this chipset (975), the upper mem dividers put to much stress at the northbridge due to tight latencies, so the solution may be to put more voltage at your MCH. This is a board to run 1:1 if its overclocked.