For the CPU, focus more on the overall performance benchmark ratings rather than just gigahertz speeds. As a guideline, look for PassMark scores of at least 9,000+ for smooth physics computations. Popular models that meet this are Intel Core i5/i7 chips and AMD Ryzen 5/7 chips. Other CPUs can also be used, including the Intel Core i9 and AMD Ryzen 9 processors, but these are overkill and won't benefit the simulation performance. You will only waste CPU performance (and probably money).