Hardware: Macbook Pro 13” Retina late 2013, Monitor 4K, 27” BenQ PD2700U
Software: SwitchResX http://www.madrau.com
Result/Bottom line: Using SwitchResX software allowed me to use 2560 x 1440 resolution at 60Hz refresh rate and the monitor kept the sharpness and detail of the full 4K...