There is actually software for the N900 that's designed for this - eCoach. According to the info on Maemo Select:

http://maemo.nokia.com/maemo-select/...ations/ecoach/

"Keep track of all your sports and outdoor activities with the GPS-based eCoach application. With eCoach you can get the most from your workouts by monitoring your speed and distance in real time. You can also use the built-in training diary feature to track your progress as you work towards your specific training goals.

eCoach supports Open Street Map, Google Earth, and Virtual Earth, enabling you to view your routes on the map and share them with friends at a later point."

No cadence, but is it that critical for you? As for battery life, I guess we'll have to wait and see, but you could always attach an external power source, such as a battery or generator hub (perfect for those epic audax rides).

EDIT: According to reports of the eCoach presentation at the Maemo Summit, the program's also compatible with Bluetooth heart rate monitors (straps). Not that they're easy to find, but still.