It takes the 945 PD to get at the 3800x2 price/performance and performance/watt. There is no reason to get any PD's. Unless your budget Absolutely demands it (then get a 805 or 915), or if you will definitely upgrade to a Core2 in the future and thus get a PD with a Core2 capable mobo.
Otherwise, get a $50-$70 mobo and get a very decent 20% cpu oc on the x2 3800+. You would probably need to get a higher cost PD board that will oc nice and oc the cpu to 4ghz to get a similar oc/performance increase.
IMO, there is no reason to get a PD unless you will definitely be upgrading to a Core2 down the road. Otherwise, the cheapest X2 will give you very close to the same results as the fastest non-ee PD. Just MO.
Jason