If I go direct it's 13 miles each way, during nice weather I extend that to 18 or so over some very hilly terrain, including one long 30% grade climb. Starting out from home in the suburbs and ending in the city. Average overall on my CAAD8 was 16mph, on the Mendota it's 13mph on a heavier bike carrying lots of extras (first aid, tools, wet weather gear, etc).

Many times I need to bring in extra clothes (if not already at work), my laptop & charger, lunch, etc. so I moved away from the CAAD8 to the Mendota to run a rear rack with bags which is awesome! I do not like carrying stuff on my back.

I have been doing this for 3 years and love it, cycling has really changed my life for the better.

Old commuter was a Cannondale CAAD8, new one is a Gary Fisher Mendota: