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#11
That may or may not be an issue since the RAM will be running at 6400 (800mhz) possibly requiring less voltage ie It won't need the full 2.3
Unfortunately, one pass of memtest is far from sufficient in determining stability. The general rule of thumb with memtest is:... also a full length memtest with all 6GB installed ran without issue, and there was nothing wrong.
a few passes for quick tests ie. testing adjustments, 12hrs for a good test and 24hrs and your golden - but it's never a 100% guarantee. I've had RAM give errors at the 8-12 pass area.
With memory timing, it's the CAS Latency timings that are important. For example mixing one module that has a CAS latency of 5-5-5-15 and a module that has 6-6-6-18 would cause instability.
You don't have to buy modules in kits, but it's more important to match the CAS latency. It is possible to adjust the timings so that all ram modules are the same, however it can be a hassle.
I'd ditch the 533mhz for now, and concentrate on matching and getting the 2x2GB modules working first. It also eliminates the need to have all four dimm slots filled requiring any NB voltage adjustment.
Another thing to look for in the BIOS, would be to ensure that the "memory remap feature" is enabled.
For the BIOS itself, have you checked to see if there is an updated version?