It's not really so much an issue to run CPU's from the same batch, just CPU's with the same stepping. This used to be a real issue with the Pentium PROs.
With Pentium II's and Pentium III's, it doesn't matter so much. I've built and tested dozens of dual-CPU PII and PIII systems, and I have seen dozens more built and tested by co-workers. We have never had a problem with mismatched steppings on the CPUs, and our warehouse people do mix batches quite often. (I know, I know, so much for ISO9001 compliance) Honestly, we just don't bother to check the steppings anymore.
I personally have a dual PII-450 system built from spare parts, and it sits and compiles code day after day with no hiccups. Both CPUs came from a disorganized collection of used parts that came out of systems returned to us for RMA. I'd be surprised if both CPUs are from the same batch or were even manufactured in the same country.
Kelledin
"/join #hackerz. See the Web. DoS interesting people."