Get the EPoX EP-9NPA+Ultra, that will save you enough money to buy the 3500+ AND the 7800GTX.....but personally i would get a BFG 7800GT. Great brand and i dont think $100 is worth it freom the 7800GT to the GTX....but thats your call. The GTX is a great card....
That way you can have 3500+, 7800GTX, 2GB ram....and thats about as good as it gets.
the first thing to downgrade is the RAM to 1GB....2GB wil give you a small boost but only in certain games and not much of a boost. Your money is better spent getting the GTX and a fast cpu....maybe the 3700+ San Deigo then havign 2GB of ram.
They are actually way good.....the bottom set rated for the highest speeds, but would be the most exspensive. The top, rev 2's, are going to be the best buy. They will be the cheapest and should OC like a beast...to around 320fsb i have seen before.