I have tried changing the GPIO output speed and then toggled the output and monitored it on a scope. There is a slight increase in rise time with the speed set to 50MHz, but otherwise very little difference. Why is this?
What kind of load to you have on that pin? Is it connected to anything? Depending on the load you may not see any (or much) difference. For example, a pin with no connection or one driving a high-impedence/low capacitance load won't show much difference. A pin driving a low impedence and/or high capacitance load will show a big difference.
