IANAL, but this. When someone is threatening/attacking you and they do not display or use a weapon that could cause death/GBH, your defense is still going to rely on reasonable and articulable fear of death or GBH. Will law enforcement upon hearing your statement believe you were justified to use deadly force? The DA's office? The jury? Keep in mind that even if the person you shot is a through and through dirtbag, their family is going to be crying on the news and calling you a murderer. It would be foolish to dismiss this as having bearing on your case. Pressure to prosecute can make your life miserable.
Motive intent and opportunity to cause you death or GBH will also factor in. Did the attacker threaten to kill you? Why did they do this? Did they act with force that could be reasonably construed by a lay person to cause you death or GBH?
From here it could branch of into thousands of what if's. That would be a disservice to the main point in disparity of force. The attaker has no means to cause you death or GBH from more than arms length. Unless you're literally backed into a corner from which there is no escape, un-assing the area and regrouping from a secure location is the best option. You can always catch your breath faster than you can clear a post shooting investigation.
