Assuming every thing is right and tight what should one expect to get for average mileage for this 5-cylinder? Assume a 60/40 highway/city mix. I'm looking into buying this car for my 17 year old daughter and was wondering what the average driver could expect?

The reason I wonder is that in driving the last 1500 miles in my 87 SDL I've averaged 30 -31 MPG using 7oz. of Power Service per 20 gal. tank of fuel. This mileage is amazing to me as it easily beats my 4 Cyl. 92 Izuzu PU by 5 MPG. Could I expect a 16.7% increase in a car with one less cylinder? The 617 is 2.5 liters as opposed to my 603 3.0 liter right? Any experiences and opinion are welcome. Thanks all.