The SUper Pershing was worth nothing really - the gun was big and long, yes, however IIRC with APCBC rounds it didn't perform very well compared to the 88mm L/71 Kwk43, and the loading time was horribly slow ! As to mobility, no, the Tiger Ausf.B was even more mobile than the std. Pershing, and the Pershing, believe it or not, was even less mechanically reliable than the Tiger Ausf.B.
The bigger gun didn't do anything for the Pershing, it was oversize for the tank and ruined the balance.