Hi I have a new 24" AL iMac (2.4 GHz). I'm working with 3ds max and Autocad 2007 in Windows XP, and Photoshop and InDesign in Leopard. I have 3 GB ram in my iMac (1x1 GB and 1x2 GB). My question is, would an additional 2 GB block (Total 4 GB) make a noticeable difference in performance? Is i worth it to pay like 50$ for the last GB?