Can anyone explain, in simple terms, the REAL difference between different grades of paint? (i.e. BM Contractor Line, Moore Style, Collection...... Para Professional, Premium and Ultra,.... Pittsburgh Speedhide, Pure Performance, Manor Hall etc etc) Apart from the price I mean. I have to opportunity to paint with MANY different types of paint and depending on the project, some of the contractor grade paints coat much better than their expensive counterparts....I've gone back years later and the job still looks great....does anyone know the difference really??