I'm looking to replace my 4+ year old iMac. I use it primarily for editing photos in Photoshop, but I am not a heavy user. Just curves, sharpen, maybe a few actions here and there. I know anything is faster than my 4.5 year old iMac. I am not interested in the 27" but I can't decide whether to get the 21.5" 2.5GHz model (the base model) or splurge the extra $300 on the 21.5" 2.7GHz model. Your thoughts and opinions would be most appreciated! (I did try to do a search but I think my search string is too short) Thanks!