Well, after putting on around 1,000 km on my 245/40R20 size PS AS4's, I have to say that the energy loss is not very significant relative to the last set. That tire, that my brain was calibrated to previously, was the Pirelli P7 in the same size. I thought the Pirelli P7 was fairly similar to the OEM Michelin in 19" that came with the car. So, given I went to 20" from 19" (which should have been an energy hit in itself), I don't think I'm doing too badly. I don't do enough regular trips to really have a baseline to work from, but a round trip yesterday in 19 degrees Celsius weather with a few areas of rain, resulted in 199 Wh/km. Speed was between 100 and 110 most of the way. That feels about right given the speed. A 90 kmh trip on flat roads was giving me around the rated 171 previously. I'll have to take a drive like that sometime to compare, but I think I'm within 10% or less of the P7s. So far so good.