Well, I installed Windows anyway and it appears to work. Not that I'm in the habit or ignoring other people's really helpful and kind advice or anything, just that I like to test things out
EDIT: From an HP support document (
http://h10032.www1.hp.com/ctg/Manual/c00257064.pdf)
Based on the information available on the Intel website at the time of this writing, Intel supports mixed steppings of processors only under these conditions:
• All processors in a system must have identical family and model numbers as indicated by the CPU ID instruction.
• All processors in a system must operate at the same frequency; that is, at the highest frequency rating commonly supported by all the processors.
• All processors in a system must have the same cache size.
• The processor with the lowest feature set (stepping) must be the bootstrap processor.
Note also that for the Pentium II Xeon and Pentium III Xeon processors, Intel does not support the Functional Redundancy Checking Mode (FRC mode) in servers using a master and checker pair of processors with different steppings.
I guess it's all good given that the speed and cache size are the same, and the older stepping was already installed as the bootstrap CPU. Might swap them to see if it breaks.