If you are driving a stick shift car how do you know when to change into 5th gear?

Normally you have to listen to the RPM rate to know when to change into ANY gear on a stick-shift/manual transmission car. Changing between fourth and fifth gear isn't any different from changing between, say, 3rd and 4th. I wouldn't bother keeping too much of an eye on the RPM meter, because if you listen closely the engine will tell you when it is necessary to change the gear.