Best efficiency of any aircraft

Hi all.

I did an extensive search on fuel efficiency of (large) aircraft on
the net.

What I found was the 757-300 of LH-Condor at 3.2 l/100km for passenger
flight and the Antonov AN 70 with 125 g/t-km for freight.

Do you know any more efficient ones? (I know that flying longer would
lower efficiency, so I take the numbers as "averages")

Apart from that: would lowering the speed/altitude of flying give
better numbers? Both of these planes can fly over Mach 0.7.

Thanks for your answers

Jonas