I do not know much about the Gigabyte graphics cards but I can tell you the typical configuration on a Club 3D 260X
Here is the card configuration;
1x DVI-D Single Link which it has a maximum resolution of 1920×1200
1x DVI-I Dual Link which it has a maximum resolution of 2560×1600
1x HDMI™ 1.4a which it has a maximum resolution of 4096×2160 30Hz
1x DisplayPort™ which it has a maximum resolution of 4096×2160 60Hz
Now, the main advantage of the MST Hub due to its 21.6 Gbps of bandwidth is that you can split the signal and you can make several combinations from a single DisplayPort output.
For example, you can split up to 4x 1080p signals from a single DisplayPort source.
In your case, I will do the following;
Use the 2560×1440 display on the DVI-I Dual Link port and the 3x 1080p screens with the MST Hub.
If you choose not using the hub you can use the following;
1x 1080p screen on the DVI-D port
1x 1080p on the HDMI port
1x 1080p on the DisplayPort using a Single Link Active adapter (cheaper than the dual link adapter)
1x 1440p on the DVI-I port (needs to be Dual-Link) to support the 1440p resolution.
The great advantage since you have the MST Hub is that you can use up to 6 displays (3 from the MST Hub through the DisplayPort + 3 on the rest of the available ports 2x DVI + 1x HDMI)
I hope this answer your question.