You think that the 2011 35i numbers are going to be that markedly different from the 2010 30i numbers? The 2010 numbers are 15/21/18 not 17/28/23. I have a 2003 X5 which has the same EPA numbers, and I routinely get 14 in town and 20-23 on the highway, so those numbers are probably spot-on. I know you converted, but that's way off -- 5mpg is 27%. The 19/26/22 to 22/31/25 is still off, but only by 13%. The 2011 for the 35d should be exactly the same for the 2010 since the car is basically unchanged.
For gallons, I think you should just stick in the US numbers instead of converting.
Can you add a column for 'km/miles per tank'? For me, its not so much about saving money on the fuel ($400/yr? eh), but how much farther I can go on a tank of gas. Give me 585 miles baby!