Managed to get my hands on a SAMD21 Zero clone and run the benchmark in #1 after converting references of Serial to SerialUSB and am surprised at how slow it is, especially the analogRead.
I have added results to the first post but for reference here, they are repeated.
Arduino Zero I/O Speed Tests Over 50000 Iterations. Compiled Using Arduino IDE v1.8.7
Digital Pin Write Takes About 1.6234 Microseconds.
Digital Pin Read Takes About 1.0264 Microseconds.
Analogue Pin Read Takes About 423.2541 Microseconds.