2007 but that was a different time.
In 2009 he had one of the strongest teams ever seen in the sport so his team had the pace set as they liked all race. These conditions make optimum performance easier. What's telling is that he he was very dominant in the TT's as well as the mountains.
2011 Giro was the most impressive to watch, mainly because it was day after day of impressive mountain performances. Not sure he would of won by 6 minutes against an in form Andy Shleck though; lets face it an inform frank schleck would have been a better opponent than Nibali, Scarponi and the rest.
There are so many variables mention by everyone already in the discussion the only way to tell would be to get hold of the power numbers but for some reason I don't think we will