Couple of thoughts...
1) In your initial trial you won't be facing the bad guy's attorney, but the state prosecutor. If there is a following civil trial, then you'll be talking to the bad guy's attorney or his family's attorney.
2) The prosecutor or the plaintiff's attorney in the civil suit can try to make whatever claim they want. Nothing says they can't try to say you used lethal force when such was not justified by a reasonable fear for your life.
3) An attack with a knife is absolutely, unquestionably, a lethal-force assault. That is plenty upon which to try and establish a self-defense claim. If you can show that the attacker had the ability, and opportunity to put you in jeopardy, and showed a clear intent to do so, then a reasonable person would decide they had to fire their weapon or face death or grievous injury.
3) Meeting a gun with a knife is not "excessive" force. You don't have to meet step-for-step up and down a force continuum. If you're faced with a potentially lethal attack, meeting it with lethal force of your own is reasonable.
4) No shoot is a "good" shoot, until the DA or jury declare it to be so ... so no one can say that you will definitely be exonerated of wrongdoing after a hypothetical violent encounter. You just never know.