You will notice pretty much no performance gain by adding 1066 ram.
You will however notice a good chunk of performance by adding another 2GB of ram
Personally i would recommend an ATI Radeon 4850/4870 for the GPU.
As for the Intel Quad Core, if you plan on playing game's such as GTA IV, Far Cry 2 etc you will notice a good difference but it depend's what graphic setting's you want to run at, if you want to run them on the higher setting's then Quad core is the way to go.