gigabyte n650sli-ds4 and RAM problems

[Nuke]

Setup:

2x2 gb ocz reaper 4.4.4.15 at 2.1V
E6600 cpu
gigabyte 8800GT 512mb x 2 SLI config
n650sli-ds4 with latest release 7 bios
enermax infinity 720w psu
32 bit xp pro, sp2

in fairness I think I have an issue with the mobo not the RAM on this one but any help to get it working would be great. I have another reaper kit on the way, the plan being to run 64 bit vista business and 8gb ram.

I used to have kingston hyperX ram and I could never get them to work in dual channel mode, if I install them for dual channel the system won't post, it's just plain dead. In single channel mode it works, however I got 667mhz speeds only, they are rated for 800mhz.

Then last night I install the reapers and same deal for me, dual channel is a complete no-post. I tried single channel as with the kingston and it was very unstable. I use stock voltage and clock for cpu, stock voltage for everything except ddr which I put up to 2.1V as rated for the reaper ram. Still very flaky, I can start windows and I can start office type programs but with many crashes and memory-related error messages. After a while typically bluescreen. Starting games they crash to the desktop straight away, WoW, Crysis you name it.

So I install one 2gb reaper in memory slot 1 and that works like a charm. Then I tried clocking it a little still at 2.1V and got it up to 850mhz but unstable as hell. Unlinked the ram in bios so the cpu is now at 333x9 mhz and the ram at stock 800mhz and this is very stable (at 2gb that is) and this is where I'm at.

I've tried to locate the tRFC settings for my mobo but can't find them, it's not under the other latency settings anyway.

My guess is the mobo, the northbridge gets smoking hot and it just can't be healthy. Having said that, it was always this hot with the kingstons so I don't think it's specifically the 2 ram units causing problems (although the kingstons ran at 1.8V) but more to do with the 4gb size. I've never tried more than 2 with this board. Should I use that SPD tool for it or am I just missing the bios setting?

Also I'm using SLI which is probably a factor. Is this config along with 2 sticks of 2.1V ram just causing a mobo overheat or am I wrong? I will fiddle later with a more barebone setup using single graphics, no overclock again, no soundcard and just see what the ram will give me. That tRFC setting would be nice to have though I have a feeling it would help to increase it.

Any ideas what to do differently?