I'm thinking that is too vague. It takes precious little time to rack a slide while bringing a gun up from a holster, in fact, maybe no appreciable extra time at all.
Correct, and there is another point to go with that. First, right, it does not take any appreciable extra time to rack the slide during the presentation. We actually had a course at the gun club a few years back that had the shooter fire two separate strings of fire. The course of fire was identical except for the fact that one string started chamber empty and the other started chamber loaded. The average difference in time to first shot was less than .20 second. For some shooters, the chamber empty was actually faster on some presentations, but nobody found it to be much slower. And if the big concern is "how fast" the way you carry the gun (IWB.OWB, position of holster, on or off-body, cover garments, etc.) will impact that time as much or more than having a round in the chamber or not.
The other point, and I think the bigger point, is "If there is a difference, does it matter?" And the answer seems to be a rather resounding "no". For it to matter the incident has to break down into a very narrow time frame where you still have time to draw the gun, but don't have tome to chamber the round. If it is on either side of that very narrow 1/4 second (estimated) time frame it does not matter.
About the only legitimate problem is the one-handed issue, and apparently it isn't much of an issue. Throughout most of our autoloading handgun history the usual carry made has been chamber empty. If there was a big problem with this, we would have heard about it. We haven't.
From a pure gunfighting position, chamber loaded is better. However, there is lots to life besides gunfighting, and taken as a whole chamber empty can be a viable solution for certain people in certain situations. Either way, it doesn't matter much. My $.02