I tried data elements again, which sort of lead me in the correct direction. Ended up finding that I couldn't use predefined data elements for this, due to the timing of when the data element is set & when change event fires.
I ended up having to add a custom condition to the rule that populated a data element (not predefined). Below is some sample code for anyone trying to achieve the same thing.
var selectEl = document.getElementById("dropdown-to-get-selected-option-text-from"); _satellite.setVar("selected-option-text", selectEl.options[selectEl.selectedIndex].text); return true;
I was then able to use the variable in the action part of the DTM rule. Hope this helps anyone trying to do the same thing in the future.
Cheers Wayne