With this kind of rig , i'd say that you have to wait for Core i7, for many reasons:
("i7 800"=2.6Ghz , 4 cores;8 Threads) and for the price its listed;284$ (or expected to be lower than Q9550 which is about 350$ .
Core i7 uses triple channel ,meaning that it will use the full potentials of DDR3 unlike the current DDR3 thats in the market right now.
and last you'll use X58 chipsets
its brand new , plus gives ya the capability to over clock each core independantly(thats if you want to overclock) on top of that intel claims that each core overclocks it self automatically based of process power you want
hope this help ,