The first one, sizing, is a calculation of the amount of work to be delivered. Expressed in Function Points, StoryPoints, Use Cases Points, Class/Method Point or using equivalent sizing metrics.
The second one, productivity, is an estimate of the teams capability. Expressed as Function Points delivered per man month, hours needed per StoryPoint, Velocity, or equivalent productivity measures.
PSV will address the two factors in both classic and in Agile context. The latter one covering lean and adaptive processes.