I'm trying to decide whether to go with the glass roof or not. My main thing is I'm an efficiency nut and it surely adds extra weight. I'm trying to figure out how much the impact would be - do these numbers look right? Standard car windshield: ~25kg? Glass roof: ~100kg? Standard roof panels: ~20kg? Difference: ~80kg? Mass increase: ~5%? Highway mileage decrease: ~1,5%? So, 3mi/5km? Does this sound reasonable to people here?