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),.