Not standing out much from the crowd when I say that I think the A4000D in a tower (specially made for it such as the Mirage4000) is just as sharp as the original A4000T.
Pros and cons way in favour of the desctop in the end I think but then I am a bit based as I've never owned a real A4000T (just seen a few) but have owned several towered A4000D's.