It sounds like the unofficial BIOS lacks support for Intel Enhanced SpeedStep technology (EIST). Your chipset appears to support it, which is why the original T7700 worked. The CPU will work pegged at 2.60 GHz just fine. I can't say how long it will last as they are already decade-old parts, and no one really knows how they were treated beforehand. However, all CPUs are tested to run under full load for a considerable amount of time before they are approved with meeting the specification. Under these conditions, the T9500 would be operating at the same variables as your own. Perhaps find someone capable of modding the BIOS to ensure that nothing was broken with respect to EIST.