Complex sentence: The performance difference between a Pentium III at 1.13 GHz and a Pentium 4 at 1.3 GHz would have been hardly noticeable, so the Pentium 4 clock frequency needed to be approximately 1.15 times that of a Pentium 3 to achieve the same performance.
Split into simpler sentences: The performance difference between a Pentium III at 1.13 GHz and a Pentium 4 at 1.3 GHz would have been hardly noticeable. So the Pentium 4 clock frequency needed to be approximately 1.15 times that of a Pentium 3 to achieve the same performance.