From my driving, 4 kids and wife in the van, I can get 40-42 miles before ICE kicks in, I do turn off AC, but leave the fan working (we're in the 60's for now so its doable). I haven't tried putting it into neutral, but half tempted. For me I tend to be very smooth with the accelerator, and utilize the regen as much as possible.
Buuuuuut, I think when we're talking about regen or even acceleration, we need to consider more than just motor efficiency. The higher the current the higher the heat losses, you can't escape it, unless engineers designed everything for max current, which would be make the entire system much more expensive and heavy.
Everything from conductors to controllers and of course the battery will see performance dip when under higher load. I think there's definitely a balance point where that current draw becomes inefficient.