Looking to move from a windows based machine (Q6600 quad) that is getting very slow when using Lightroom 4. I am looking at a refurbished iMac 27-inch 2.7GHz Quad-Core Intel Core i5 for $1359. Not the fastest machine I know but I think a good upgrade for now. My current machine has 4 1T drives in it. 1 of the drives I have my pictures on it which alone is almost 500GB (raw files). What is the best solution for an external drive? I understand it has a thunderbolt port so I am guessing I would need to buy a thunderbolt drive to store my pictures on it. Is the transfer rate going to slow me down with edits etc? I am wondering if I should buy a Mac Pro instead for the ease of drive installation? Tried one years ago.. a beast.. but instead went back to windows at that time.. Thanks!