Clock speeds depend on many things, like thermal limits, power draw, what instructions are used, how many cores are active, whether the integrated GPU is running (for OpenCL) if it's enabled, …
2.2 GHz is guaranteed – without AVX, with you only get 1.8. 2.8 GHz is possible, assuming there are thermal reserves, power consumption is not hitting a limit, etc.
Ok, so all cores could run at 2.6 GHz momentarily but it would probably start thermal throttling pretty fast. And maybe not at all if the cores were using power-intensive units.
2.2 GHz is guaranteed – without AVX, with you only get 1.8. 2.8 GHz is possible, assuming there are thermal reserves, power consumption is not hitting a limit, etc.