I have the 'd', so I can't help with actual comparisons. But I bet the next questions someone that is in the know will ask is how many miles are on the car? They seem to consume more gas at the beginning.

I know that my 35d is getting somewhat lower mileage than what people have posted here, but now that it's past the 1000 mile mark, it seems to be doing better.

Also - it's strange that your math and the on-board computer are so different. I wonder if anyone has experience with that.

Lastly, I assume you are filling it with Premium. Lower octane will yield lower MPGs....

Sorry I can't be of more help. Surely someone will chime in very soon.

Cheers!