Hello, this is my first post here. I'm using a 13-inch Retina MacBook Pro (Late 2013) with Intel Iris 5100 graphics running Mavericks (10.9.5) with all available updates and have connected a Dell P2415Q monitor, configured to SST mode, using the supplied mini-DP-to-DP cable. As expected, the system defaults to 3840x2160 at 30 Hz. I have attempted to increase the refresh rate by using SwitchResX 4.5.2. However, I can only get up to 40 Hz using CVT-RB timings; aiming for a higher refresh rate causes all screens to go black and I have to hold the power button to turn off the MacBook. 40 Hz is marginally better than 30, e.g. I can see the mouse cursor is a little less laggy/jumpy than before. When using Linux, I can get 3840x2160 at 52 Hz or 3520x1980 at 60 Hz using the exact same system, cable and monitor without any problems. These two modes take full advantage of the pixel clock limit which is 450 MHz for Haswell-ULT according to Intel. The monitor's OSD confirms it is operating at these modes when I set them and the mouse cursor movement etc. is much smoother than at 30 Hz (in fact, I see little difference between 52 Hz on the P2415Q and 60 on my other monitors). These tests have been performed with the MacBook's internal display being enabled and the P2415Q connected to the Thunderbolt port closest to the MagSafe port, nothing was plugged into the second TB port or HDMI (so two displays in total). As I've not tried Yosemite or El Capitan yet, this problem may be due to Mavericks (my experiments have proven it's not a hardware problem) but has someone else come across this oddity?