The fastest guys I've run into are usually Australian, I ran into a few Italians that were pretty quick too. Every country has great racers though. Why do you wanna know anyway? You can't challenge a whole country y'know dude.
This question is so weird and unnecessary... most people will just come up with baseless answers or root for their own country. Stranger still because GT6's online mode isn't enabled yet, and here we have a thread asking which online drivers are the fastest, posted in the GT6 section of the forums.
I feel like we're getting to the point where we're actively looking for any possible questions to ask, no matter how random.
I've found on a global stand point there's not just one fast driver but a very large group on the VR tracks. You put them all on a real track more than a forth would be cut. From there it come down to that fastest driver on that day or year. It's comes to who you are behind the wheel during that moment.
I'll agree with most of these replies. Every country has fast drivers, and this thread/question isn't all that necesarry. Throwing this out there though, Fins often give me a run for my money.