I wouldn't be concerned with speed, the fan motor is not an issue.I have 2 ac infinity 6' oscillating fans. I've used others, but to me, these aci fans run much smoother and quieter than the others I've used. I alternate each one, 12 hrs at a time, and never push a higher speed than 5.
Imo, like anything else, pushing something to the max limit, is always going to wear it out faster.