If you look at the Technical Product Specifications document from Intel (Page 23), it shows a bit more detail. In particular, when using both the mini-DP and HDMI you are limited to 1920x1200 via HDMI. You can do full resolution if you daisy chain off the mini-DP to two monitors.
In my testing, I wouldn't feel comfortable using the product for those resolutions. In testing 4k and multi-monitor configs, the machine gets pretty hot and performance isn't that great for non-static content.