Much, much cheaper here: http://www.komplett.co.uk/k/kl.aspx?bn=10483
That's where I got my 165 from. (Got it for £75, only a few weeks ago..)
If you are not overclocking, then the 185 is ok, but is also rather expensive for what it is. The 170 is good.
The opterons also have 2mb L2 caches, 1mb per core. I think most of the X2's only have a total of 1mb.
Opty 170 is my vote!
You should find good OCing and stability.