AMD Athlon 64 3000+
This AMD Athlon 64 3000+ 'Venice' is based on the E3-stepping. Later versions came with E6-stepping as well. Differences are minimal: according to AMD's revision guide on Athlon 64's there are issues with Enhanced Write-Combining and several DDR/memory-related addressing problems with the E3-stepping that the E6 doesn't have. I'm not sure if these (noticeably) affect performance or overclockability.
The E3's are identified by Ordering Part Number (OPN) 'ADA3000DAA4BP'. I have two E6's with OPN 'ADA3000DAA4BW'. One used chip and one unused in it's original box.