I have a late 2014 5k iMac, with a 4 GHz intel i7, 32 GB of 1600 MHz DDR3, and a 4 GB AMD Radeon R9 M295X video card.
The crop tool is laggy. I select it, and try to drag the corners of the preview area, and it lags, jumps around and is imprecise and slow.
This is odd, as making a rectangular selection is smooth and works fine to then select Image/Crop.
Also in Adobe Lightroom the crop tool works smoothly, with it's preview overlay.
Why the disparity?
I haven't seen this bug anywhere else listed in your forums or elsewhere online, so I wanted to report it now, to ensure that future updates have it resolved, as I don't want to have to buy a new computer in order to update my OS, in order to run the latest version of Photoshop that's not BETA, or an old version that won't recieve new features.