I've done a few long journeys in the ioniq 38kw now and when cruising along the motorway it's surprising (ish) just how much more efficient the journey is if I keep it <70 as opposed to just a few mph >70. Today I covered a return journey of 130 miles and on the way there I set it at 68. On the return leg I thought I'd speed up a bit and just watched that battery disappear. Back to ECO+ and 68 on the last leg haha.
Headwind makes a big difference as well, but I have noticed that around 66-68 seems to be the most efficient speed (high speed), that is GPS speed not the car instruments, once you hit 73-75 you require so much more power to drive you thought the air it becomes much less efficient.