DisplayPort's biggest advantage is G-Sync support. GSkid mentioned it briefly above, but compared to all the other factors discussed here, G-Sync is huge.
G-Sync works as advertised and completely eliminates frame tearing and frame judder. The difference for Railworks is dramatic. Train motion is silky smooth like we have never seen before, even when frame rates fall in dense areas. The other cable types may eventually support G-Sync, but until then, DisplayPort wins the battle by far on this feature alone.
( PS - I'm running GTX-970 into an Acer XB280HK )
