The short answer
A moderate dose lowers LDL by 30 to 49%, a high dose by 50% or more. Each 39 mg/dL drop cuts heart attacks and strokes by about 22%.
So the higher your LDL and your risk, the more you gain. Someone at 20% risk gains much more than someone at 5%, from the same pill.
Source: CTT Collaboration, Lancet 2010; 2018 AHA/ACC cholesterol guideline.