Upgrading dual CPUs - is stepping important?

I'm planning on upgrading a 2010 dual quad-core Mac Pro to dual six-core CPUs (x5675). I remember back in the old days of dual CPUs (think Pentium), you had to have the same stepping in both CPUs in order for the machine to be able to boot. Is this still the case? Have their even been multiple steppings of this CPU? I can find CPUs in matched pairs, but it's sometimes cheaper to buy them individually.

Thanks!
I'm answering my own question (should have...

Upgrading dual CPUs - is stepping important?