You're right.
The processors are not specially screened, or anything.
Of course, all the ones with 512 KB L2 cache will become Athlon 64's, as there are no 512 KB L2 cache Optereon models.
Some with 1 MB L2 cache become Athlon 64, some Opteron, some Athlon 64 FX.
The dual-core ones of the same die would become Opteron 165 - 180, or 865-880, or Athlon 64 FX-60's
However not every chip can hit even 2.4 GHz, Most of them will do 2.2 GHz regardless, some do 2.6+ GHz, and they become the higher end parts
depending on market demand only.
Putting the Opteron 'badge' on a few Socket 939 chips (as 'real' Opterons, even the 100 series ones, are Socket 940, and have coherent HyperTransport links to other CPUs) was the best thing AMD ever did. All the Fanboys have more 'choice' and can rave about their 'Opterons' (Albeit 100 series, single CPU socket, Socket 939, usually without ECC RAM. Registered RAM isn't really an option on Socket 939 boards, but Unbuffered ECC is).
Opteron 100 series (Socket 939) were meant for 'blade' style servers, using Unbuffered (vs more expensive Registered) ECC DDR-SDRAM. The downside is they can't be upgraded with huge capacity Registered DIMMs. These servers are not in need of a high clocked processor, and certainly are not overclocked at all. They'd be passively cooled
if possible.
It is simply staggering how many AMD fanboys do not even read or visit the AMD website:
http://www.amd.com ; and read the documentation.
Also have a good long hard look at:
http://multicore.amd.com ; aswell.
No special instruction set differences are present at all.
RIGHT HERE, Explains how the Socket 939 Opteron 100 series, differs from the Socket 940 Opteron 100 series:
http://www.amd.com/us-en/Processors/ProductInformation/0,,30_118_8796_8806~85257,00.html#85258