There's been a few who have done that...IIRC, expect your mileage to drop some (maybe 1-2 MPG?) Bigger rear contact patch=more rolling resistance. The front's are the same size as the factory tires, so no change there.
I have them on me premium with upgraded suspension . I have experienced no mpg loss . If anything I'm consistently getting better mpg city . Have to clean them a few times a month as the brake dust accumulates . I just use a damp micro fiber cloth .