Q: How much of an aero difference does it really make?

Developed and validated in CFD, the splitter used with the rest of the aero package delivers a net aerodynamic shift of -434 N at 150 mph and moves the balance from front-heavy toward neutral. That 150 mph figure is a standardized comparison point, not a driving suggestion. At real freeway speeds the same lift-reducing effect is present at smaller magnitudes. What you feel is a more planted front on long sweepers and during passes.