I definitely use every gear, any given day I drive..... (If I hit the highway) which I do Monday to Friday.
Iin the city... I don't really reach 6th gear. Generally 5th is the highest, and in the city even that is a stretch sometimes. Given that city limits range between 30-60km/h depending on the area.... Pretty obvious why I don't reach 6th. Factor in traffic, and I'm no where near 65km/h which is around the point it doesn't lug in 6th for me.. ( For you down south, the city speed limit is 31 mph in most cases, - 37 mph in some of the suburbs here ). But you can expect to rarely reach that in traffic.
That said, I don't "always" shift in numerical order, either up or down... (necessarily). I may, if it's that consistent of a gradual change..... But just as often, I'll bypass a gear or a couple. Whether up or down.
As far as 6th goes, yeah... I don't really use it until at least 65kmph.. Can feel the lugging noticeably at 60. (note - that is not miles per hour.)
I don't really watch RPM anymore either to be honest... I shift based on feel/sound and a sense of speed.... You get used to the sound & feel and eventually based on your senses... can generally pick out the right gear for the job.