Fitcontributer Track and Speed data points

Hello, I'm thinking of an app concept to Record maximum value of  Speed for a given track, and display in connect IQ graph as track vs max speed recorded on that track. 

How can I find out the update rate for the toy box track readout.

I'm trying to create a graph of maximums, and then display. Does connect iq allow custom fields in both x / y axis, and could I use some kind of array to save the max data or copy the array at the end of session to fit , for the recording?