This analysis might benefit from a multivariate regression. You mention a few different explanations for why performance differs and if you could get solid numbers for those you could try teasing that apart.
Also a small note: the axis on one of your plots alternates between 4% and 5% increments whilst holding the ticks constant. Maybe because of rounding?
Also a small note: the axis on one of your plots alternates between 4% and 5% increments whilst holding the ticks constant. Maybe because of rounding?