As everyone keeps stating, go the i5. The i5 comes with the ATI 4850 graphics which is a $100 upgrade in itself (if I am not mistaken), and so the i5 is really only another $200 upgrade and with that you get twice the number of cores. Further mhz vs mhz, core vs core, the i5 beats the Core2duo. I haven't kept up exactly how much faster the i5 is compared to the Core2duos (with cores/speed being equal) but the i5 would at least make up for the 400mhz difference in speed and you still end up with 2 more cores. With the advancements in Snow Leopard (i.e. Grand Central Dispatch), OSX has the ability to take advantage of more cores with a greater ease/efficiency. The i5 will hold its value longer.