[dcb]

...and power brakes like vacuum.

Hard to get a good reading on energy content of fuels. What btu/gallon figure do you use for diesel and gasoline?

Here is one, admittedly less than perfect, way to look at the gains from diesel, epa figures for similiar cars:
2001 vw golf 4 cyl, 1.9 L, Manual 5-spd, Diesel : 35 city 44 hiway
2001 vw golf 4 cyl, 1.8 L, Manual 5-spd, Premium: 22 city 28 hiway

however I have no problems making over 50mpg in my gas 1996 saturn in the city, since putting a stick shift in it and p&ging the snot out of it. Hard to have the patience to beat 45mpg on the hiway though.