Every two years I upgrade my computer. My last update was in February 2011. I've been looking at two computers - a Mac Pro with an Apple Cinema Display and an iMac. I like the Mac Pro because of its easy upgradability and future-proofness though out this decade, which I can't say of the iMac. However, I also like the iMac because of the built in screen and reduced cost from not having to buy another monitor. What do you think I should get?