A graphic card has the following limitations:
- a maximum amount of ports, in the case of Nvidia, that's 4.
- a maximum resolution per port, in the case of the GTX980, that's 5120x3200
- a maximum texture size, which is 16384x16384 on most modern GPUs. This in turn translates to: don't worry about it.
When using a TripleHead or Datapath, you use up only one of your available ports. These are extenders, so they take a larger image and then use their own hardware to divide it over its multiple outputs. Since the max resolution per port of your card is well over 4K, you are able to extend a single port to four times HD on a Datapath or three times HD on a Matrox (if its firmware supports that). Your computer will see the extender as a single, larger output, in addition to the other outputs you have connected.
When using a MST hub, you can change a single into three outputs. Each of the outputs will show as an individual discrete display on your computer. It's important to remember that a MST hub does not extend your output. This means you are still limited to the maximum number of outputs your GPU supports. Adding a 3-way MST hub to an Nvidia card with a 4 port maximum, means you will only be able to use one other port on the card. The other two will be disabled. For this reason, MST hubs are better suited to add more outputs to a single output card, like laptop GPUs.
For Resolume, it makes absolutely zero difference if you are using an extender to create a bigger output, or are using multiple discrete outputs via the card itself or MST hubs. On both options, you will be able to use all the available features for slicing, masking and blending.