Its when I fall behind that I go silent, and thats when I'm at my most fierce. If I'm talking/shouting I'm annoyed, if I'm dead silent then I'm going to give the guys in front of me the most pressure I can possibly put on them and take any tiny opportunity I'm left before they have time to react. I'm not neccessarily calm, I'm just in my own element, every truly serious race I usually end up silent if I'm chasing and just doing what I do best. If my assault on the lead is halted severly though, I do get impatient and make an opportunity out of nothing by simply being unpredictable without being outrageous, whilst often on the verge of screaming at the guy infront if they have no right to be there and are losing me time. The silence allows me to listen to the other guys revs, so I know what he's doing, if he'll be shifting soon, and allow me to predict as much as I possibly can about what they'll do next and how I can get past them.
Again its a trait I carry across to COD4, when I snipe (which I take just as serious if not more so then competitive GT5P), I fall silent once I get into it, listening for footsteps, gunfire, anything.