This question would be better posied to IBM as the answer relates to how the BIOS configures the system
In general, the newer stepping of the CPU will contain fixes for errata as out lined in the processor spec update.
The BIOS likly contains work-arounds for these errata that may be impacting system preformance.
Based on the note in the event log, IBM's BIOS just treats both processors as if they were the older version and continues to load the work-arounds.
It is best to run with both processors at the same stepping. You may want to consider moving the processors so that the blades contain match pairs just to head off any potential issues.
Seems you're using two Xeon 5100 series processors, mixing B-2 (CPU ID 06F6) and G-0 stepping (CPU ID 06FB). On the processor side this is supported, but you may want to check with IBM if it's a validated/supported configuration on their server. Also see AG111 in Intel® Xeon® Processor 5100 Series Specification Update.