It is possible to drive two 4K monitors plus the Surface's screen by using the dock's mini display port and the Surface's mini display port at the same time. The Surface can't drive a 4K monitor at 60Hz, but it can at 50Hz with a custom resolution. Everything was pretty smooth, even at 50Hz. I used two 27" Dell P2715Q 4K monitors with the following custom resolution: 3840 x 2160 @50Hz, Timing Standard: CVT-RB. A custom resolution can be created by installing the latest Intel graphics driver and running the Custom Resolutions tool in the HD Graphics Control Panel. Pictures or it didn't happen... : ) See attached.