mixing CPUs

Recently I bought a HP DL385 Opteron server at auction. It has an Opteron 265 1.8GHz dual-core CPU and is designed for SFF (Small Form Factor) SAS disks.

A friend told me that S-ATA disks would work in it and so would a faster Opteron CPU. I bought 3 S-ATA disks which work fine in a RAID-5 array. Unfortunately when I tried booting with the second CPU installed the BIOS said that it detected a CPU speed mismatch and would halt.

If anyone knows of a way of swapping Opteron 265 CPUs so that I can get a pair at the same speed then please let me know. I'd prefer to swap the 1.8GHz one for a 2.2 GHz one if possible, but the other way is also an option.