Could have up to 25% better fuel consumption see http://www.airliners.net/aviation-forums/general_aviation/read.main/6289311/1/#1
and from wiki (needs citation) "The Super Seventies were a great success: roughly 70% quieter than the 60-Series and, at the time of their introduction, the world's quietest four-engined airliner. As well as being quieter and more powerful, the CFM56 was roughly 20% more fuel efficient than the JT3D, which reduced operating costs and extended the range"
and (max ferry range):http://www.airliners.net/aviation-forums/general_aviation/read.main/467439/
6690 kg/h (25% better) to 7136 kg/h (20% better) fuel burn for a 767-200 sized aircraft (250 pax max) (DC-8-63) which comparatively has a 4 140 kg/h to 4 750 kg / hr fuel burn makes it viable depending on cost and needed range, quite a lot better than even latter Soviet designs such as the 767-300 sized (300 pax) Il-96-300 which burns 9 680 kg / hr.
So while somewhat flawed to go by max pax due to door restrictions, etc. It can still give an idea to floor space:
16 to 20 kg/h per max pax for 767-200ER and 767-200 (best and worst case)
25 to 27 kg/h per max pax for DC-8-73
16 to 18 kg/h per max pax for 767-300ER and 767-300 (best and worst case)
32 kg/h per max pax Il-96-300
the -71 should be more efficient than the -73 but be very short ranged and the -72 would be the long range but the bad CASM one at 34 to 36 kg/h per max pax which is slightly worse than the Il-96-300, which I managed to have success with from the 90's to now the 2000's but am phasing out in favor of the Il-96M ( 23 kg/h per max pax) and the Il-96-400 (fractionally lower than 23 kg/h per max pax, mostly for fun due to short range and late availability).