Theres a guy on cmpg with an echo hitting numbers in the mid to high 50s and recently had a 60 mpg tank. Its a very nice car.
Some aero info.
Echo:
Cd - .29
CdA - 6.57
xA:
Cd - .31
CdA - 7.26
xB (1st gen):
Cd - .35
CdA - 8.77
xB (2nd gen):
Cd - .32
CdA - 8.37
Yaris:
Cd - .29
CdA - 6.36
FYI, I made a list of many other cars here:
CdA list