It is obvious that in general, the more notes a piece has, the more difficult it is to memorize, and that the quicker those notes are played, the more difficult to up to tempo. However, when playing a slow movement of a Mozart Sonata, you are working with completely different difficulties that can be equally as challenging. Through my experiences, I find that I am able to play some very demanding concerti with reasonable ease and stability. However, I often find myself using an equal or greater amount of concentration while playing some classical music. I find that at a slow tempo it is very difficult to get the most precise phrasing, due to the disintegration of the sound that I am unable to control. Surely this is obvious to all...