Max speed is close to 120. This was tested in the past. Link:
From 116 on you are at max speed. With max speed it is important to move / rotate fast enough. Otherwise there will be air hits in between which void some of the additional speed.
150 is the speed stat limit of the game. Likely for technical reasons. Such high speeds have no additional effect anymore. For example 118 speed topaz hammer gets no benefit from speed brews.