IMO You have less info to process on line so you don't have to take as much time, live your looking at the player in person looking for tells etc, building tension for subsequent cards to come.
i think good players tend to have a good idea of how they are going to react if they miss/hit the flop or how the hand will progress, i have sometimes made the call in my head before the guy has made his mind up to check, bet, or shove. Other times the All in Vs Fold is such a hard choice, if you have doubts then fold, now i know that i have totally ignored that and called anyway LOL. sometimes you hit call and then think NOOOOOOOOOOOooooo before you' ve even seen the cards.
If i find I'm about to make a big all in call esp in the money or near the money i ask myself the following question/s........
"Do i need these chips now, and will i mind going out now?"
as for the reaction times i try not to let it influence me too much, after all some people have poor connections.
And prefer to be the one going all in

i find i can make my mind up very quickly