I am on a early 15" Macbook Pro Retina Display with dual Intel 4000 and Geforce 650M GPU.
I know the early MBP 2013 doesn't natively support it. However I was told by this forum and others (posting screenshots with 4K@60hz) that there is a workaround where I am able to achieve 4K at 60hz or at least 50hz.
I already bought the Mini Displayport 1.2 to HDMI 2.0a active adapter and a 4K monitor.
I use SwitchResX and I have done the pixel clock patch.
I just can't get over 30hz in 3840x2160 when outputting to the 4K monitor. I even tried 50hz and no luck.
I know there is a workaround to get 60hz or at least 50hz. I am on El Capitan.