Link Transmission Rate and propagation speed are measuring different things.
Link Transmission Rate is the amount of information that can be pushed through an interface at one time, and measures the volume of data that can be moved in a period of time. (If looking at an Internet connection, think Advertised speed of the connection)
Propagation speed is the speed with which the information travels (if looking at an Internet connection think ping time between the 2 points). Propagation speed would be the influenced by the speed at which the signals can be switched and the distance between the switches - for example it takes at least 60ms from a signal to travel from LA to New Zealand due to the speed of light (pings are > 120ms, because a ping goes there and back again)
Larger Link Transmission Rates can increase propagation speed by allowing data to not queue up at the exiting interface.