The fact is the X2 series, and all AMD processors, are to highly priced for what they offer right now. The Intel Core 2 Duo systems are performing much better for the same money. If AMD wants to compete they need to drop the prices on there current parts and bring out faster parts to replace the current top priced ones. At the current time it makes no sense to spend the moeny on the AMD chips if your building from scratch (aka mobo, CPU, ram). A E6700 will beat most (I'm not sure about all) of the FX AMD line for considerable less. Then add to that the fact that your getting the newest chipset that will only have faster chips coming out for the next few years. Not to mention quad-core chips are supposedly going to be using the same 775 chipset when they come out in 07. Rumor is that even the eight-core chips are going to use the 775 chipset in 09. I think getting a setup that supports Core 2 Duo is the only smart thing to do right now if your going to spend the money.
For the original poster. By the time you go to buy prices are going to defenitly be different. Not to mention your going to be able to get an SLi board based off the nForce 590. I'm waiting for the DFI board as many others are. Many feel its going to be the most wanted board of 06 and into 07. If history serves true it will be overclockable like an SOB. I'd keep my eye on it. With $1,200 by december your going to be able to get much better stuff then right now so it's hard to advise on that. If at all possible get the E6600 or higher for the 4MB cache over the lower 2 models.
Good Luck!