well i dont know about that, but i do know that some of the x2's were crappy opteron steppings; i, myself, had an x2 3800 whose stepping was known from less-than-stellarly overclocking opterons. whether it was a rebadged x2 or actually was a rebadged opty i couldn't tell you for sure, but i can confirm that some steppings show up on both.
but i'm pretty sure it was an older one, and considering age, you should keep in mind that they don't even make 939 cpu's anymore, at least as far as i'm aware, so any opteron you'd buy won't be really that recent.