I use a 2013 Mac Mini, base model (4GB RAM, 500GB HDD), upgraded to 16GB RAM, with two 27" Apple Displays. It replaced a 3-4 year old MacBook Pro 13" (base model) that was really struggling with LR2.6 - I'd quit all other applications before opening LR. Now with the Mac Mini, it's doing quite well: I can leave iTunes, Firefox, Thunderbird, Terminal, and Preview open while running LR5.2, and I think it's even been decent while also running Parallels so I can use Windows on the Mac. I wanted an SSD but wasn't willing to pay the difference to get it preinstalled from Apple; I'll swap one in later.