This is one of the reasons I question CC. It CAN be reassuring to be locked and loaded..but when you look at encounters and stats and such you have to wonder if it really does any good. VS the risk of other issues (legal, gun being stolen, etc).
Like carrying one in the chamber vs having to rack the slide. Look how many 'accidental' discharges there are, people shooting themselves, their cars/car seats, etc. That seems to out number the times I've heard/read that there wasn't time to rack a slide.
Again, practice practice practice till it's second nature. Carry only ONE gun so you're not having to think 'ok, which gun do I have today?' - if you always have to rack the slid to shoot then you just do it like second natore.
If being ambushed I don't think it will matter either way. If you can't draw the weapon, it won't matter either way. If all you have to do is brandish to scare them off, it won't matter either way. It's .3 second to rack a slide, if that (with practice), and I would hope you have more time than that to decide if you need to shoot and attempt to injure or kill someone.
And consider, when you're amped up, surprized by the bad guy, your trigger control may be lacking...you may shoot when you don't intend to.
Start watching Active Self Protection (ASP) on Youtube. John has hundreds of live feed videos of deadly encounters. I am not saying he is the expert on what happened or should have happened, or that this is in any way training for folks watching. Just watch the videos to see just how fast people get stabbed, shot, mauled. You have very little time to react from ambush....and if you are being attacked it is almost always from ambush.