Wait a minute, not sure if it was 6.7 orthe other way round coz mixed driving I am also getting 7.6l/100km~8.2l/100km so. Normal to moderate driving still averaging 420~480km per tank. (I know you don't like my per tank measurement >.<) About same as my vios so I don't want complain too much since this is a 2.0cc car.
Anyway, I got my car back from my friend's workshop, and he said that it wasn't due to my driving because my front skirting was not secured properly. Apparently they just screwed it in with a rubber bolt without the washer (a metal ring), and thus it was only a waiting game because no matter what it will eventually fall off, due to the design of my skirting, which has high resistance to wind since it doesn't have any holes. He said if one were to push it down by hand with some force the whole thing would have dropped off without much resistance.
It made sense to me because my car started the flapping sound first, and it connects as I started driving at those speeds at a more pro-longed time this time round on a longer journey. I would not go above 140 on my normal commute even if it was during midnight, and even if I do it won't be longer than a minute or two. So after 1 hour or so, driving at above 160kmh really took a toll on my skirting. Design flaw? Defect? Poor QC? Either way it feels like anytime my car might fall apart and there is nothing I can do since external issues are not covered and I have to fork it out no matter what. Most shit thing is I didn't think of taking pictures.
Anyway I called my SA and told him about the issue. He said he will pursue the matter for me, and find out which panel did my skirting etc etc. I told him I just want the skirting to be replaced at no loss, IF NOT then just touch up my current skirting so it doesn't look so shit.
Hope anybody who got their bodykit from mazda go check and see if their front skirting is attached with a washer; don't kena like me

Hopefully just me kena.
Anyway, my friend damn nice, he didn't want to accept my money. So now my front skirting is firmly in place now. Just can see very minor scuff marks at the bottom, and one side can see the washer and nut coz that side fell off and cannot be recovered, probably still somewhere in Cherating, lol. The bauxite there damn 96 btw.

I think it must be 6.7L/100 km. If 7.6 on highway better go and check! Since you drive fast 6.7 would be considered normal.
I was offered body kit or RM1000 cash. I took the cash. I think our M3 look pretty good without body kit but that's just my personal opinion. Not a fan of skirting anyway as it lowers the car and make going over bumps more difficult.
Didn't manage to get the Castscreen working but that's OK. Sort of lost interest in it and it's still a work in progress anyway.