The problem is that you are 5'8" and have an inseam of 26". I am 5'9" and have an inseam of 29". Standing over bike isn't the only criteria. That said if you are in between a small and medium it is probably easier to fit the small to you, longer stem/more seat setback. Also, as Tusky mentioned, the small will have shorter crank arms that may help the fit with shorter legs.
John