jtran987, again thank you for sharing this story with us. I too am very happy this turned out well for you and your girlfriend in terms of your safety/security and any legal ramifications. Please understand any questioning of your choices/tactics truly is just Monday morning quarterbacking and is an attempt to learn with everyone else following this thread. Please know that your "goodness" (for lack of a better term) is not being questioned, only the choices you made are being dissected so that everyone may benefit from your experience.
With that said, I still think you were a bit quick to pull the gun based on the information you've provided. There are two additional steps I feel you could have taken before the "threat" was real enough to warrant pulling your firearm (both have been mentioned previously either here or in other threads):
1. Hold out your off hand, palm toward the men in the classic "stop" motion and say very loudly and assertively "STOP! Do not come any closer." If the men continue walking toward you at this point, then I believe you've exhausted all possible de-escalation possibilities and pulling your weapon is justified, IMHO. In your OP you stated that you asked "very loudly what they needed" and they ignored you and kept approaching. This is close, but still not the same to me as an assertive vocal "STOP!" and hand motion.
AND/OR
2. Go a different direction away from your car (back toward the restaurant, down another street (as long as it's at least as well lit as current street) and see if the men continue to follow. Again, not seeing this first-hand it's difficult to know if there was time to take an evasive manuveur such as this. But it should be attempted if possible. If these men just happened to decide to head in your opposite direction with no ill intent, then they will walk past and situation is over. If they intend harm, then they will likely follow you.
It cannot be overstated that the above is strictly "best practices" and tactics that can be used if the situation is right. I was not there so don't know if these tactics would have been best in your particular situation. Just food for thought. In my mind, based on what you've told us, even if the cops gave you a hard time and/or arrested you, if I was on a jury I would not have convicted you of aggravated assault in this case. My only reason for repeating some of these suggestions is that the goal is to avoid the ride AND the rap.
Again, very happy this turned out well for you and VERY pleased you were carrying and able to defend yourself.