hi,
There is a note regarding this memory on the OCZ web page, that may be of interest,
(All Modules are tested in two module kits. Due to additional bus load, four module configurations may have to be run at lower frequency and relaxed latencies for stable operation. Test specifications are based on dual core CPUs only. If quad core CPUs are used, higher bus thresholds and core arbitration may necessitate lowering the memory frequency below tested specs.
***OCZ EVP (Extended Voltage Protection) is a feature that allows performance enthusiasts to use a VDIMM of 1.95V without invalidating their OCZ Lifetime Warranty.)
Have you tried upping the voltage? to get it stable,
Regards