The reason why it's not charged as attempted murder is that it's difficult to prove the specific intent to kill. That's always been so, it's not some softy modern approach. You might think that saying 'You'd better not be here when I come back, because I'm going to kill you' rather suggests that specific intent ! (I'd agree). But, being realistic, it's a fact that people often say 'I'm going to kill you !' as a threat without any real intent to do that, and they do it in fights and in attacks without that intent. Now, it's a waste of time charging attempted murder and having a jury arguing about the niceties of meaning and intent , even if the witnesses are definite those words were said, in those terms, when you can charge s18 wounding. He can get life for that and the case is straightforward. It's better to charge wounding with intent rather than gbh with intent because a) it's stabbing, a definite wounding b) gbh with intent gbh requires the jury to decide whether or not gbh was inflicted and there's no point in their wasting time discussing or arguing about that, either
As to sentence, he's looking at 10 years minimum. [See the guidelines given in the link above] He may be eligible for an indeterminate sentence, one where he has to serve at least a set number of years, specified on sentencing, but can't be released even after those unless he's not seen as a danger to the public any more.There are aggravating features plus the public interest in safeguarding doormen and others whose job involves keeping the peace, and which exposes them to attacks from thugs.