I would recommend to daniemare to go for the 27" with the i5 and fusion drive, then max out the RAM to 36 GB aftermarket. This should service your needs very well for 3 or 4 years. I am about to receive my new iMac Tuesday [about 4 weeks from my order] as a replacement for my Mac Pro 2,1. I really wanted a new Pro, but got tired of waiting for Apple to crank out an actual, modern, state-of-art replacement. I use Lightroom and Photoshop, which is not really too demanding, but specced out my iMac all the way [except for RAM] anyway, so that I'll be comfortable keeping it for 5+ years.