Honestly, I cannot tell the difference between 2 and 3 !
I don't blame you. Neither can I! In fact, I'm pretty sure that there isn't a difference in meaning (although there is a difference in
use).
In both sentences, the latter clause is a logical deduction from the former. A different way to express both sentences is:
It is not possible for the meat not to have been slow-cooked, given its tenderness.
If this is something that is imagined to be spoken informally, I think 3 best represents what the speaker is really trying to say. Rather confusingly, in informal speech, it is quite natural to omit the conjunction
that in
so ... that ... patterns. In writing, it is generally advisable not to omit the word
that in
so ... that... patterns.
There are two difficult issues here, as I see it.
1) Style differences between written and spoken discourse. By this, I mean that a written transcription of what is imagined to be a spoken utterance belongs to the world of spoken, not written discourse. My earlier advice about the use of semi-colons was meant to be taken with this in mind.
2) Whether we would recommend using a comma to represent those spoken utterances that omit the conjunction
that in
so ... that ... patterns. I personally don't think it's necessary.
After saying all that, it is quite possible that alpacinoutd intended there to be two separate sentences. If this is the case, the word
so takes on a different role (as a simple intensifier) and correspondingly has a different intonation. Without having access to the pronunciation, we cannot be sure which was the intention.
alpacinoutd—could you tell us a little more about what you mean to say? How exactly are you trying to use
so?