I got to say that Im a bit 50-50 still on my conroe upgrade.
Sure, I can convert the Vids off my camera to dvd, many times quicker than my AMDs could, which Im sure has to be 4 or 5 times quicker. Many things are quicker on the conroe which is brilliant, however, I havbe lost the ability of having a reliable system, this thing is seriously pants when it comes to playing HalfLife Epsiode 1 ( Although HL2 vanilla plays peachy ) and I have had nothing but problems with need for speed lot, especially UnderGround 2... In fact last week I finally got hold of underground 1, and had to uninstall U2 and MW just to get it on, put U2 back on and now it wont even load up! - Utter drivvel.
The other week, I got so annoyed with mine that I brought my AMD back down and thats once again my main PC and the conroe is upstairs and just being used for my video convertions only!
So, for me, it was a waste of time bothering.
Glad I did though, dont get me wrong, and I hope to resolve these issues sometime, but its certainly the worst PC I have ever had for not being able to run things properly at this time.
As for the original Post, both will clock fairly well, the 3800 has a 512K cache, or rather 2x512K and the Opty has 1MB so I would go for the opty over the 3800, but it depends on what you can get them for really.
And James Miller is right too! - If you already have a good single core, then going x2 wont suddenly make you twice as fast.
I went from a 3200 Winchester @ 2.8 to a 3800 and pretty much struggled to get that over 2.5 and I found it was a bit of a poo CPU really... No improvement in games or at least not enough to notice and I wished I had just gone for a fast single opteron to be honest... Which I also now have.