After a monitor upgrade, I discovered that the DVI to Mini-DisplayPort adapter I used with my KVM and a 2013 Mac Pro didn't work at 2560x1440. Although an mDP cable from the monitor worked fine, I was reluctant to give up the easy switching that enabled me to share a mouse, keyboard, and monitor between a nMP and PC. Several posts indicated that only a few adapters in the hundred dollar range would allow this resolution to work on a Mac using DVI to DisplayPort, and while I can't verify that, I found a much cheaper alternative that does work.
The StarTech MDP2DVIMM6BS Mini-DisplayPort to DVI Active Adapter is a 6 ft dual link cable and works perfectly at 2560x1440 60Hz connected to my Aten CS1782 KVM switch and nMP. List price is $53.99 but can be found for $30-40 from numerous retailers.
http://www.startech.com/AV/Displayport-Converters/Active-Mini-DisplayPort-DVI-Cable-6ft~MDP2DVIMM6BS
The StarTech MDP2DVIMM6BS Mini-DisplayPort to DVI Active Adapter is a 6 ft dual link cable and works perfectly at 2560x1440 60Hz connected to my Aten CS1782 KVM switch and nMP. List price is $53.99 but can be found for $30-40 from numerous retailers.
http://www.startech.com/AV/Displayport-Converters/Active-Mini-DisplayPort-DVI-Cable-6ft~MDP2DVIMM6BS