What the Mavic will handle, without getting blown away, and what is comfortable and safe are two different things.
It also depends on the purpose of the mission, and how far away you intend to fly.
For me, since I usually do landscape videography I like to keep it to 10-15 max, better even lower. But for those just wanting to cruise around they will tolerate 20+, but I cant imagine that being a lot of fun.
It's also easier to fly in winds near the coast as it is much smoother than inland with trees and terrain turbulence. You will have to experiment with what is comfortable for your needs, a little at a time.