Heh, I'm coming into this thread a bit late, but I thought the 3700+ could use a bit more support. Basically, unlike whats been said in this thread, the 3700+ still has A LOT of life left in it. Yea, a Dual Core that costs $100 more is going to last longer, but if you're looking to spend $100 less (and still get higher clockspeeds >_<) then the 3700+ is an excellent choice. It can handle anything thrown at it without problems, and it will be able to keep up with the GeForce 8s far into their lifetime. The advantages of a Dual Core are currently non-existent. Games utilizing both cores won't come out for a LONG time (6-8 months, or more). So you're paing $100 more for something that you wont use for the better part of the year. Not only that, but the 3700+ can overclock as well as, if not past the Opteron 165. You said before that you wouldn't be "overclocking the h3ll out of anything." Well, you'll have to or the Opteron is practically pointless. So to recap, you're paying $100 more for something you won't use for atleast half the year, something that has a lower clockspeed, and something that you could get the gaming performance out of for $100 less...Not very smart if you ask me.
Dual Cores are great. Just not that great right now. I'm more than happy with my FX-55-like 3200+, so a 3700+ will almost definately get to FX-57 speeds.
You're going to tell me that a FX-57 won't be able to keep up with GeForce 8s?
Save the money and put it towards a 7800GT or something instead. I would recommend against a 2nd 6800GS.