well it really depends. X2 is gonna give enough performance for some people to stay over at the s939 camp. id say build an x2 rig or even a venice/san diego rig, they are still doing great in the way of performance.
i wouldnt say its the best choice, but its alright. personally id get a 3000+ or 3200+ venice, oc it like no ones business. it will cost less and run cooler and overclock more
they run soo cool that an xp120 does good enough of a job to usually get a maximum overclock outta them, barring the use of Phase Change or high end water.
a 3500+ venice is usually only very slightly more expensive than a 3200+, and you get a bigger multi. With a bigger multi you are likely to get farther on air than with a cpu on a lower multi. So if you are getting a 3200+, I recommend a 3500+ instead. However a 3000+ is also a good buy, but if you don't lan on investing a bit more money into better than stock cooling then you might want to stick with a 3500+. I say 3000+ b/c you can get em for about $120 (ewiz.com)