It is easy to estimate this.
- look at Apple's "Activity Monitor" while doing what you normally do with your Mac. Look at the average CPU utilization. Let's say it sits at 10%.
- Look at the increase in speed of the new CPU. Let's say this is 20%
- Multiply the two together to see the real-world speedup. In this case, it would be about 2%.
What this means is that if your normal workload does not stress the CPU, a fast CPU is not very important. But if Activity Meter told you that the CPU utilization was about 95% then a 20% faster CPU would give you a 19% real-world speed boost.
It gets worse. Some things can not be sped up. For example, I am right now writing a design document for a software project. A faster CPU will not allow me to write faster. In general, most tasks we do can't be sped up because the speed is limited by the user.