I use only Sunoco 94 and I get 350 - 400 kms a tank, although most highway with a mix of stop and go. My mileage is consistently around 14.6L / 100kms, but it gets even worse when I am driving hard.
Well worth it though. Looks like the E93s are a little worse on gas with the extra weight.
2008 E93 M3 - SSII, 6MT, 19", EDC,...