I'm very glad you said this. My EDC carry is either my G23 or G22 (for those who aren't familiar with Glock, they are both .40 cal). I have a BUG or one that I wear with short summer wear that is a Sig P238 (.380). It has an external safety on it, unlike the Glocks. Since I predominantly carry one of the Glocks, I practice with them more. I was at the range the other day and had my P238 holstered and I drew to fire at the target and neglected to hit the external safety. That concerned me A LOT!! I am now considering replacing that firearm (and I love it, it's a remarkable tool) and getting a Ruger LCP. My muscle memory was so ingrained to draw and fire that the Sig, no matter how great a weapon it is, will not suit me since it is mechanically different from what I'm used to. I must get a firearm that does not have an external safety. This is me.... I'm not recommending to others to make sure you get a firearm without an external safety, what I am saying is, whatever your choice of firearm is, practice with it so that you can react with it; develop your muscle memory. My muscles are already learned to not flick a safety, therefore having one is an obstacle for me now, just like someone who decides to carry chambered one day, and not the other day. Are you going to remember, today I do not need to rack the slide or today I must rack the slide in a pressure situation? I've proven to myself even in a non-pressure situation I wouldn't.
Just as Kramer stated he practices lifting his shirt with his left hand, drawing with right as he clicks off the safety until it is a routine for him, this is what you need to do with your firearms. Most people have the will to win, when what they really need is the will to prepare. Tactically, practice practice practice.