Question for native speakers - Would I be correct to assume this expression is used when you're getting upset and do not wish to listen any further?
Why not "ya"? Just joking. We use it quite often, I think in this case it is emphasizing the "suficiente", and it sounds more natural to use it if the speaker is upset, there are other sentences like "haven't you done enough?", we also like to add a "ya" to this (even if there's not an "already" in the English sentence) just to have more emphasis, as in: "¿no has hecho suficiente ya?"
We use the word ya so much that some people even feel like they have to say it twice, they put one at the beginning and another one at the end, but that's very colloquial. I think in most cases it will sound more natural to use it at the beginning of the sentence, sometimes when we use it at the end it takes the meaning of now, for example:
- Yo lo quiero ya. (I want it now).
- Voy a hacerlo ya. (I'm going to do it now).
In those cases ya is a short way to say ya mismo, which is the informal version of ahora mismo (right now).
"I have heard sufficient" was accepted, though that's not proper English in my book. In that sentence, sufficient is describing how I heard, therefore it needs to be an adverb; not an adjective. So, even though it's not a literal translation, I think the best translation of meaning would be "I heard sufficiently" E.g. if I was in an audience and someone asked me if I could hear well enough where I was sitting. After looking at the discussion & seeing that "I have heard enough" is the intended translation, that makes more sense, but it's not really equivalent in meaning to the literal translation. Oh well.