Intel now sell their CPUs with an advertised Core Clock speed, and a Turbo Boost (up to) speed.
As well as this, thanks to SpeedStep (dynamic frequency scaling), a CPU will often underclock to conserve power and reduce heat. Therefore, a CPU rarely sits at its advertised core clock speed anymore; it's constantly changing in realtime between its minimum clock speed, and its Turbo Boost speed.
Take for example, my dual-core Core i7-4650U:
- Base clock: 1.7GHz
- Minimum/idle clock: 0.8GHz
- Turbo Boost (with both cores active): 2.9GHz
Here's I tried to post a graph displaying the clock speed of my CPU over the time it took to write this question (using Intel Power Gadget), but I need 10 rep to post an image, so you'll have to take my word for it: the frequency was rarely (if ever) set to 1.7GHz.
If I earn 10 rep in the meantime, I'll upload the image :)
So, my question is: what does the base clock speed of an Intel CPU actually indicate anymore? Personally, as a consumer, all I really care about is how low (for power savings) and how high (for performance) a CPU can be clocked at.