[wagonman76]

Im not sure what a larger bore would do. I know that I have had 2 examples of the same car which gets better mileage with a larger engine. The 3.1 is a stroked 2.8 and in my case gets 2-3 mpg better in the same car driving the same roads.

90 Pontiac 6000 wagon with 3.1 got 30 highway
89 Pontiac 6000 wagon with 2.8 got 28 highway
Both have 4 speed automatic with 3.33 final drive
Both have same options and are basically the same car

89 Celebrity with 2.8 got 29 highway
Same 89 Celebrity with 3.1 got 32 highway
Same 4 speed automatic with 3.33 final drive

A stroked engine gets the benefit of a longer lever arm in addition to more displacement for extra torque.

These are just my experiences. Other cars may differ greatly.