I'll throw my $0.02 in here. I've kept track of the mileage achieved with my 2012 35is since I brought it home in January of 2013. On strictly highway trips, throwing away the highest and lowest recorded numbers, I've always gotten between 27.0 and 32.8 mpg.
If you're just cruising and keep your foot out of the turbos, my guess is you'll be okay.
