So now I'm guessing CPU and memory doesn't have much to-do with mining,

Well i can do a dedicated low power mining rig like yours,

Athlon II
2gb DDR3
4x 5830s
850W Sliverstone

for around $1000 AUD so less than half of the one i proposed earlier.

Would that be more economical or would cutting down on the CPU and memory of the previous and use
6990s be more economical ?

I'm very new to mining and its about the time of year i upgrade my PC and i was looking into
building a dedicated mining PC.

Here are the proposed specs:

AMD Phenom II X6 1100T
Gigabyte GA-990FXA-UD7
8GB Corsair DDR3
Powercolor Radeon HD6990 4GB x2 maybe a third later on this year
Silverstone Strider 1200W Gold
Most probably running windows 7

inc HDD and Case it comes to around $2500 Australia Dollars

I would like to know how profitable mining would be with a rig like this?, would it be better to mine
in a pool or solo mine ?
What would income figures look like ?

Thanks,