By using steel and concrete you can increase you post spacing to extreme lengths.
This whole is 3'x3 (36"x36") and takes 3 guys about an hour to dig one hole. (picture below)
This post is to show what is possible. The one thing to remember is that this make the job much more labor intensive and costs more in material. On this patio it was several thousands more to have the steel framing done. It is great but in the end you get what you pay for... hope this was helpful.