my input about inside vs. outside temps, it's basic thermodynamics. if you are exposed to high temperatures long enough, the inside will eventually be almost if not as hot. if your aircon is running then they will sort of average out depending on thermal conductivity of all media in contact (tint, glass, metal, air, etc.). even the heat from your engine will seep in, but it's mitigated by the firewall.

now, heat transfer have different types. I would suppose the tint best blocks off heat from radiation. but aside from that there's conduction and convection where the tints can only do so much to minimize since it's too thin. even latent heat from living organisms and sensible heat from your gadgets contribute to the "room temperature" inside the car, but these contribute significantly less heat compared to other sources. in the end, having a good aircon system is the most important factor, followed by infiltration (heat from the engine and outside the car seeping in due to depleted/worn out firewall, opened windows, and seal condition of door rubber lining).