Just upgraded from old Evinrude '75 135hp to not as old Evinrude '83 175hp ($400 deal of the decade) in my Center Console, and finished fuel tests this past weekend.
Ran out 30 miles Sunday to a few wrecks in about 70' of water. Total miles traveled were 90, and used 36 gallons, (48 gallon tank), so right at 2.5mpg. 60 miles of the trip was at cruising speed of 30mph @ 3800rpm. 6 miles was no wake river cruise, 900rpm, until we hit the gulf. The rest was slow speed looking for bottom at various time. It tops out at 43mph (GPS) at 5400rpm.
Keep in mind when comparing numbers, the hp rating change in '84/'85 means this 175hp would be about the same as an '85 and newer 150hp.