Mount speed modifiers increase multiplicatively, with each modifier increasing the players Total Mounted Speed (which is "100% + Mount's Speed") by "Total Mounted Speed x (1 + Sum of Modifiers)". Non-stacking multipliers are the only exception to this formula, in which case the largest possible modifier is only applied (either the product of the stacking modifiers or the non-stacking modifier itself).
The new mount speed achieved with the Crusader Aura can be found through the formula "(100% + Mount Speed) x (1 + .20)".
[Carrot on a Stick], 
[Riding Crop]*
