I say to you this. Any Dual core at 4.0Ghz will bottle neck a 4870-4850x2 and up.
Now i would wait for p55 boards. Im planing on either getting a i3-i5, just waiting to see how things play out for them. Basicly im headed for some ddr3, Top air cooling, 32nm proc. I would suggest a Phenom II 940-955 a xtreme hpase asus board, xiggy heatsink, and some 60-40 dollar sticks of DDR3 ram. I would get the 955 to 3.9Ghz
. OR wait for sata 3 p55 boards with 32nm rape overclocking chips with ddr3 to
. Just get a 5800 something, I probable get there single fastest card setup