The 757/767 has super critical elements in it's wing design as well. Obviously the best technology of the day has been surpassed with the 777 as after- market winglets are now available for the 757. Here's a good read about supercritical wing technology.
http://oea.larc.nasa.gov/PAIS/Concep...rcritical.html
From an after-market winglet manufacturer on the benefits...
"Aviation Partners Boeing expects to Performance Enhance the majority of the 600 plus existing fleet of 757-200s with revolutionary Blended Winglet Technology. Operator benefits include: a block fuel improvement of up to 5%, approximately 200 nautical miles of additional range or up to 10,000 lbs. of incremental payload capability, improved second segment climb, enhanced operational flexibility (such as trading improved fuel burn for faster cruise speeds), improved takeoff performance out of high, hot, or obstacle limited airports, reduced engine maintenance costs, enhanced aesthetic appeal, increased aircraft residual value, and a range of environmental benefits that will equate to an economic payback period of less than 3 years for most operators."