My new Latitude E7470 running Debian's 4.4.0-1 kernel enables power saving on everything except NVMe, reaches pc8 & cc7 & rc6 & C10-SKL according to powertop. It's new, so the battery is lasting a relatively long time depending on the load. Maybe almost two hours for heavy development & testing with a busy network, projected 6-7+ hours for light reading. -- jason@lovesgoodfood.com
Another data point: Dell Latitude E7470 works (up to nvme)