Someone had commented on TWOP that they thought Tennant's Doctor was actually scarier than Eccleston's, and now I can see why. Nine had a gaping wound in his psyche, and could lose it with terrifying fury, but his anger was more reactive, emotional.
Ten has a chilly calculation underneath his genial surface. Especially with Harriet Jones after her execution of the Sycorax. He knew what the future was; three terms and England's golden age. And it no longer pleased him. And seeing everything that could be, he knew exactly where to drop the tiny stone that would change the future to suit him.
And I loved the delivery of "Witchcraft!" "Time Lord." Because it was witty banter yet he delivered it with just enough weight to remind you how goddamn fucking scary Time Lords can be.