My speed breakthrough came when I went from 170 to 175 40 years ago. Used it exclusively since except: my old Peugeot fix gear; no ground clearance, a newer Peugeot fix gear; same issue and an '80s race bike I set up as a double with 172.5s. Knees did not like that bike! I now keep the Q-factors down, ride only 175s and only triples and fix gears.