Mixing RAM, especially from different brands, isn't exactly the best thing. Plus, why is the OCZ RAM EOL (End of Life)? Typically when they are labeled that it usually means it has been superseded by an identical but superior (and often times more stable) version. It may be just that they're old (they are DDR2) but the aforementioned reasons are also possible. Check to confirm if there are similar or nearly identical versions. It may even be just bad memory you managed to purchase and needs to be replaced.
Have you checked your motherboard to confirm that both sets of RAM are compatible? Does things run fine if you only run with one or the other but not with both?
Memory can handle temps pretty well. If you suspect it may be too hot, then it's often caused by the internal temperature of the case being too hot (this also is displayed in the motherboard's temp as well). Make sure that your case has proper airflow going through it to prevent heat from accumulating.
For additional attempts at fixing this, you can try a BIOS update for your motherboard. Go to the Gigabyte website and download any possible update for your specific motherboard model. Note that it is imperative that your system be stable during the BIOS update, so reduce the amount of RAM in your system to only one set of memory if you know that will stabilize things and then run the update. Lastly, for any memory testing you may use Memtest86+
. Sure beats waiting for your system to BSOD.