Flapless T/O
I tried timing and measuring the ground roll to 150 kts both flapless and with T/O flap/slat (we take-off in mid flap/full slat, which is also one of our landing configurations and is actually quite high drag - theory is to minimise ground roll and rely on reasonable excess power, and option to jettison in the event of engine failure, for initial climb) in the Tornado sim last week. The result support NoD's statement - there was negligible difference. Admittedly not an airliner, but operating using the same laws of physics!