While the Zeb is still a great fork at 170, to me it has a pretty linear air spring and it goes through the midstroke quicker than the 38. The Fox tends to sit up in its travel a bit more, so even though both are 170, the Zeb can feel like it has “less travel” in certain situations because the dynamic ride height feels lower—especially on an e-bike where you really want that extra support.
After riding both the 38 and Zeb at 180, the Fox felt a bit flexier and didn’t really benefit from the extra ride height the way I expected. The Zeb, on the other hand, feels better at 180: the ramp is more predictable, it sits a little higher, and it matches the Zeb’s air spring character (since it naturally wants to use more midstroke). Bottom-out support is great for me with one token, and on an e-bike it just feels like the perfect setup.
If you go from 170 to 180 travel on the Zeb, you'll want to remove 1 token (I went from 2 to 1) and run ~10% less air pressure (I went from 72 to 65psi) - I'm 175lbs rider weight for reference.