Ya dude those black kidneys are looking sick, I've always had a thing for black bimmers... I was pretty close to buying a black 1995 E34 540i but it was 4hrs away and I said screw it. I noticed you blacked out the badging at the back, at first I thought you'd just debadged it.
I had a feeling I could go 700kms+ but he hiighest I've gotten to is around 680 kms/tank (with about 5L in the tank). I've done some 150-200kms trips at about 115kmh on the cruise and I'll barely use up a quarter tank, the mileage on this car has really surprised me. On average though I'll get between 550-600/tank and that's with 400 km on the hwy, so around 8-9L/100km.
Funny what you said about the sunroof... that's exactly what my mechanic said too!