Kimi Räikkönen... this would sound monotone and short, but very unique and would calm you down faster as you can say F1
PS: Translator-San would be funny, too ^^
what can this man do? woof, and the battle has been joined, and here he comes...up the hill, goes over the curve...and another curve! he overtakes the bugatti, or was that a maserati? this will be crucial, but noooooo~
don't interrupt him, for he will guide you with his commentary XD
Personally I would rather not have any voice trying to guide me through. I find it rather annoying. There are some places where voice over could be cool but in terms of guiding through the game I would not want it at all.
One of the most annoying racing games I think I have ever played was NFS Pro Street. The commentary was maddening.
If GT ever did add a voice to guide you I would hope that you could at least turn it off and quickly skip through to the start of the race rather than have to listen to someone talking about it and wait for them to finish.
Give me a plain menu and let me a press a button then go straight to the race.