Don't get derailed guys I'm interested in this thread and don't want it to get locked lol.
Regarding the holding slide of a gun... not a great idea for reasons mentioned above.
If you are caught off guard and find yourself with a gun pointed at you within one step...
#1 Drawing your own gun is pointless, you will get shot. You have a 1-2 second draw time and the bad guy has a .1 second reaction time (average). You are TOAST.
#2 Compliance and de-escalation are your friends, use them first. Your wallet or car keys aren't worth your life. (Besides you may gain an opportunity to draw and fire with the distraction they provide; see here for a real world example against multiple attackers that WORKED:
http://www.liveleak.com/view?i=f6e_1392219642)
If you think they are going to kill you anyway... and distraction and de-escalation aren't working (or the odds are way against you)...
Remember that humans have an average of .1 second response time. I catch people on this all the time when sparring (martial arts) - the person with the initiative can do amazing (and very ugly) things at close contact distances before the other can respond, even if they are expecting it.
Attack the weapon. By this I mean either the gun or the human meat-bag behind it. People can't shoot if they can't see, poke 'em in the eye. If you contest their weapon ALSO do something to hurt them with the other hand (you DO have two of them).
Pushing the gun aside and delivering an elbow to the throat/jaw/neck area can do spectacular things. I took out a guy with a knife this way once (for real, defending my life.) Put hard parts on soft parts.
The soft parts to reach are eyes, throat, nose (makes eyes water, can't see). Solar plexus strikes are great too (shocks the diaphram) but it requires training to hit accurately and the shock can be overcome if you HAVE training. Genitals are NOT reliable enough - depending on the physical state of the attacker might have no effect or actually "hulk them up" (I used to use the term "retard strong" for this but I'm trying to be more politically correct these days.)
In a hand to hand fight you have other options; knees, etc, but I train people on those to escape a hand to hand conflict - damage the other so they can't chase after you. In a gun fight that isn't an option because you can't outrun the bullet.
So remember, knock the gun aside (try to keep it from pointing at you, hand on wrist or gun continuing to push it aside) and using the other free hand HIT THE SOFT PARTS HARD AND REPEATEDLY. You have time to do this even if you are one step away because of human reaction time; by the time they realize they are in trouble, it's too late.
Human reflex is going to mess them all up here. Predator turned prey throws people off and human nature will make you DROP things uncontrollably to protect your vision and throat area.
An attacker cannot effectively engage you if they cannot see or breathe.