Not that easy. NYT data shows not only 4% increase for VaporFly, but also 3% increase for Streak. Springer is harder. Though 18 male aren't enough to prove anything, the data is quite consistent. But 4% equals to 5 min in marathon. That means that a lot of athletes from 2013-14 could break 2 hours in that shoes easily. Probably 5 min on a treadmill at 18 km/h has little in common with 2 hours at 21 km/h.