In this glossary article on multi-processing, the author concludes that the multi-processing example is 50x slower than the single-processing example - but the comparison is flawed. In the multiprocessing example, the timer is started before the text file is read and the values stripped, but in the single-processing example, the timer isn't started until after the numbers are read from the text file and stripped/cast.

Hum, good catch. Thanks for highlighting that.