More info about the mp4/17D, from a few people:

The manager of TAG McLaren Martin Whitmarsh:

As a matter of fact, the MP4/17D that we will see in Melbourne has a new transmission, new suspensions and a deeply revised Mercedes engine making an additional 50 horsepower compared to the "spec" used in Suzuka last year .

David Coulthard, the driver said:
"That car is effectively quicker than the one used in Suzuka",
..............the rest is just usual bla bla...