New pc. DDR2 or DDR3 memory?

I’m thinking of building a new PC with a budget of roughly £1100 -1200.

Its not going to be used for games, just design work. It will need to handle complex 3D dynamics such as fluid and particles and also need to render things as quick as possible.

Im thinking of getting a quad core intel cpu and a 8800 graphics card.

Im not sure about what memory I should be looking out for. I want to go with corsair but if anyone has anything else to recommend i would consider it. With £200, I could get either 4gb of high speed DDR2 or 2GB of DDR3. Since DDR3 runs at higher speed than DDR2 I wanted to know if it would be woth it sacraficing 50% of the capacity for the faster DDR3? I could always buy another 2gb of ddr3 later down the line.