I have just updated
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to include the results of the timing tests I did some time ago on some different microcontrollers. Currently data is available for PIC, AVR and an AM186 clone.
The tests don't claim to be a scientific or totally conclusive. Comparing performance is notoriously difficult and means different things to different people. At the end of the day you choose the best processor for your job ... however, may be of interest to some.