As an old time m3poster who now sometimes takes a look at what is happening here, I'll contribute to this one as you may be interested in my experience in my 997, which is a MY09 .2 C2S so has the direct injection engine.
It’s a 6-speed but after I drove a PDK recently I noticed how it changed up very early compared with my normal technique but also how much better the mileage was, so I tried the same approach in my 997.2 C2S.
So rather than changing up at 3500-4000 rpm as I was doing I started changing up at 2000rpm and just using light throttle to avoid loading the engine unduly. And one thing I found straight away that the mileage improved dramatically. From 15 or so (in US mpg) to over 20 even around town – that’s around 15.7 l/100km to less than 12.
On the track I get around 24-26 l/100km and now often see 10-11 commuting to work and back.
Maybe it’s related to the DFI engine and I don’t claim any particular wisdom on the matter but I thought you may find it of interest.