cpu - Are Intel Processors' GHz really matter?

It has been confusing me for a long time.
Say, an Intel 4th Gen dual-core i5-4200U which clocks at 1.6 GHz and up to 2.6 GHz and an Intel 4th Gen dual-core i3-4160 which clocks at 3.6 GHz.
As I see that they are both 4th Gen (Haswell), dual-core processors. Can I judge their processing speed based on the GHz given?
I was told that i5 would be faster than i3, but it wasn't explained in detailed.
Each of the core of i5 has a maximum of 1.3 GHz while each of the core of i3 has a speed of 1.8 GHz.
If they can't represent the precise speed, what are they for?