Second, although it looks like this would be a nifty way to introduce different temperatures into free energy and standard potential measurements, the T in the middle section is really 298 K. A much more complex expression is needed to even include concentrations other than 1 M, let alone different temperatures. So at this level the expressions have rather limited applicability.

Finally, a word about concentration. Your lab results clearly demonstrate that changing the electrolyte concentrations can change the measured potential. That should now make even more sense in light of the connection between E^o and K_c. LeChâtelier's Principle again... It also fits the scenario of a changing measured voltage for a battery as reactants are converted into products. It is possible to calculate the voltage (E) under non-standard conditions of concentration. In fact, such calculations can even be used to determine equilibrium constants experimentally. But that is beyond the scope of this course.