DCTs have some driving advantages over manuals - see Lincoln's paean to his girly clutch-operating leg above - but the figures are clear: manual gearboxes yield better efficiency.

Whilst I don't expect the actual figures I quoted above to be reflected in real-world driving, I wouldn't be at all surprised to see that the difference between manual and DCT is indeed present.

Another factor which a DCT cannot consider, no matter how cunning its ECU, is that a manual gearbox's computer is equipped with forward-facing oculation devices, aka the Mk1 Eyeball. A DCT transmission will make shifts that a human driver wouldn't, thus reducing fuel efficiency a little.