I think, if anything, it actually speeds up my group of 5. I have a party sheet with things like AC, skill checks, etc. And I'm generally rolling my d20 right on top of that sheet, so their AC is right there. It's pretty easy to just tell the player if they were hit or missed (and I normally also record a "touch AC" so I can give a better description of what individual misses mean). Granted, if there were regular AC changes in the party, then I'd probably need to switch to having the players keep track of that. But in an online game, I find the back and forth of numbers even worse of a slow down than in person.On the large group topic - isn't the DM keeping track of AC a timewaster? My group is typically 6 people, and that would certainly slow me down.