Before I repowered I had a 1975 115 V-4 that I bought new when I bought my then 3-yr old Seafari. It used to burn about 8 gph at 4500 rpm/22-23 mph cruise. Over the 6 trips I made to the Abaco's with it, loaded very heavy, I averaged 2.8 mpg. I used to figure on 2 mpg just to be safe and have some reserve.
I just finished a 700 mile trip around Fla. with the E-Tec and averaged 4.35 mpg, again loaded very heavy and with Bimini top up but generally running in fairly flat water relative to the Bahama trips. I usually assume 3 mpg with it for planning purposes, but the neat thing about the E-Tec is that if you get in a situation where you're worried about running out of gas, just slow down to hull speed/900-1000 rpm! When they're running in the ultra-lean stratafied charge mode they burn even less gas than a 4-stroke! I have the I-Command gages with GPS spedo and fuel flow from computer, and it typically shows about 10 mpg at 5 mph! That system appears to be very accurate . . . every time I refueled the actual fuel used was within about 0.1 gallons of what the computer said I had used!