Now that I have your attention...
So as a background, I have done quite a few long trips in the Boxster. Hence why it has over 106K. Last summer I did a 6000 mi+ trek across country for my sisters wedding. As before with the cruise control on, roof up, strait flat road, two people and luggage I was never able to break an average of 30mpg. If I recall my best indicated was 29.8 or something like that.
Not usually I could care less about gas mileage, sometimes I see how low I can get it just for fun. But this was interesting. Recently I changed the clutch out and replaced the fluid in the transmission. This is the only change that I made since last summer. Same oil, tires, wheels, etc...
Last week I drove down to San Diego and back for the holidays. Again two people and luggage. On the way down I was driving like a total ass so I couldn't really call, however on the way back after a friendly reminder that it wasn't acceptable I found myself with the cruise set 70-75, top up and even with some varied driving and AC on I was still at 30.6 until I hit traffic.
After dropping my GF off in San Fran, I came back down the 101 cruise set at 70, AC off, just me, and was able to average 32.2! Not that this is earth shattering by any means but a larger difference than I would have expected for just changing the gear oil.
Now I do have to admit that I did not use the Porsche gear oil but a formula given to me by a highly regarded Porsche mechanic. So far into the 40's it still shifted just fine. I'm not here to start a war on fluids, I'm just stating that clean fresh fluid made a much bigger difference than I would have ever expected.
Oh and still not a drop of oil used between oil changes!