Is it possible that a PC with Core i7 CPU running at 3 GHz could outperform another PC running at a higher clock speed (say 4 GHz) Core i7 CPU?

Yes, it is possible for a PC with a Core i7 CPU running at 3 GHz to outperform another with a 4 GHz Core i7 CPU. Performance can be influenced by various factors beyond clock speed, such as CPU architecture, the number of cores and threads, thermal management, and overall system configuration (e.g., RAM, storage speed). Additionally, if the 3 GHz CPU has better single-threaded performance or is paired with faster components, it could lead to superior real-world performance in certain tasks.