Basso 2006 was more dominant then Contador 2011, I´d say. He was also great in 2005, except the day he lost almost 45 minutes on Stelvio. 2006, he was great, dominant in the mountains and almost equal to Ullrich in the long Pontedera ITT.
The double, however, IMHO, wouldn´t have been possible. I thought it was possible when news about Ullrichs lack of shape came up at the end of April, just before he started his season in Romandie (:o). But if you see Ullrichs development from the Prologue in Romandie to the finishing ITT in Bern in the TdS, and regarding he still had two weeks after TdS to lose some weight and improve shape, Ullrich woukd´ve been favourite Nr 1 for the Tour.
Even if he realized the double, the triple might have been even harder. Sastre did all three GTs in 2006 for CSC, but not as a captain.
However, Basso in 2006 was so dominant, so who knows... But if you consider that even Contador said that the triple is almost impossible, I doubt Basso would have done it.