Top speed is usually achieved between 6-8s with varying degrees of abilities to maintain it. Speed still follows a parabolic curve. Thus typically you will see top speeds achieved between 50-70m for most trained individuals at the elite level. In recent times we have seen some of these segments stretch out to 8s. However, you need to also remember that those splits you are talking about are averages for 10m. The actual point at where the max speed and duration of it is unknown unless you have access to laser recordings. So when you get a split at 50m, 60m, 70m and the fastest split is 70m it could be the 60 or 50m where peak speed is achieved especially if the splits are close say 0.86, 0.85, 0.85. As there are errors with measurements you can’t say with 100% confidence where the peak speed was achieved as its an average measurement over a 10m segment.