[e2daipi]

I believe that you are referring to this[0] study. It has since been published (2011), though it's not openly accessible.

Page 8 of a presentation by the author[1] shows that out of 7 languages (Japanese, Italian, Spanish, French, German, English, and Mandarin) English is the second most information dense language, Mandarin being the most. Spanish is characterised by a fast rate of low-density syllables.

A Spanish to English comparison (eye-balling) would be that Spanish is spoken at a rate of 7.8 syllables per second vs 6.2 for English (≈ 22.9% faster). (Spanish compared as a lot of comments are referencing its simplicity)

English, compared in the referenced study, achieves the highest information rate, is spoken at a moderate-slow speed with a high information density.

[0] http://www.ddl.ish-lyon.cnrs.fr/fulltext/pellegrino/pellegri... [1] http://neukom.dartmouth.edu/docs/pellegrino-presentation-dar...