Brimstone

I did an experiment years ago on an old 4 cylinder engine (I think it was an '88 VW Fox) I got 2-3 mpg better milage with 93 or 94 octane vs. 87 octane, however cost per mile was still far better at 87 octane. And this was when it was like $1.10 for regular and $1.30 for premium. now with it being $2.00 and $2.50 I really doubt premium could be more cost effective.

As far as diesel engines go I also believe they're rated for more miles, but I could be mistaken.

The Fuelly app will show you your cost per mile and you can track it by octane or brand etc..

So far I think the closest the onboard computer has come to manually calculating it is 1.8 mpg over the real number. My last tank was 3 mpg difference (it said 26, but I only got 23), the onboard computer seems to over estimate by 10-12%.

Atvars

As I previously mentioned, Q7 has potential to reach even 5.3 l/100km (44.38 mpg). Was in fact a bit as a surprise and unexpected. Usually I follow closely what average mpg is, now just looked, and surprise, there it is...