As I reviewed the flight plan with Mike, I noticed an interesting discrepancy. The dispatcher had planned for us to fly at .84 Mach. Considering the fact that .86 is our MMO, the speed was uncharacteristically fast. I picked up a company phone and dialed. The dispatcher that answered had relieved a colleague who had just gone off duty. Apparently, the off-duty man had the 777 on the brain and not the 767. A re-crunching of numbers at a slower speed saved us 5,500 lbs of fuel.