I commute about that distance every day I can. When I need to haul stuff or it rains, I will use this bike. Since this thread needs pics, I submit this as a reference in support of using a MTB.
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1997 Specialized RockHopper, on Flickr[/IMG]
Although this isn't currently built, it could be another reference for using more of a road bike.
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104_PaTrek., on Flickr[/IMG]