I'd just like to bring the Cessna Citation X into the discussion here. This aircraft cruises at mach .91 and has a range in excess of 3000nm at that speed, making it the longest ranged Citation jet. The fuel burn for this aircraft starts to drop off drastically at altitudes greater than FL370.
Boeing says the "sonic cruiser's" cruising altitude will be in the mid 40s, and it will have a range of 9000nm.
For it's speed, the fuel burn of the Citation X is not bad at all. If Boeing is able to duplicate this kind of performance in a new airliner, they would definitely have a winner on their hands.
Here are some links to the Cessna website for the relevant specs on the Citation X.
http://citationx.cessna.com/performance.chtml
http://citationx.cessna.com/range.chtml
http://citationx.cessna.com/specifications.chtml
------------------
Safe flying to you...
[This message has been edited by Flight Safety (edited 02 April 2001).]