We started this page to catalog tests of speed for a variety of microprocessors and electronics modules. Here we define speed as how fast information can transit from external electronics into the core where microcode is running and back out again. A good way to test this is by constructing a ring oscillator, which simply sends token back and forth, producing a waveform that can be measured with an oscilloscope.
To measure speed across a GPIO layer, we use a logic level as out token.
To measure speed across a radio link, we use the smallest supported packet.