Don't forget that you're actually trying to get a certain number of "volumes of CO2" into your beer. The pressure required depends on the temperature of the beer, which means that you can adjust the psi of the regulator depending on the temperature (I'm not talking about "burst" carbonation...
When I started brewing (less than a year ago) I converted everything in Palmer's book to metric. Since then I've followed the natural progression from "extract only" to "extract with steeping grains" and now do all-grain. Along the way I realized that everything I was ordering and most recipes...