I'm not sure what you're looking for in comparing speed to cadence. Cadence is simply the number of revolutions per minute. Depending on the gear you are in your speed with differ.

You can use this calculate to estimate your mph in a certain gear and cadence. http://sheldonbrown.com/gears/

If you are asking about the proper cadence - each of us is different. The old adage is to target the 80s-90s, but this is also different based on the terrain and your body. RBR had a good little test from Max Testa on determining whether you're a spinner or masher. Need to go find links here also.

Go through your Polar book. The software should set up the computer with the max HR based on your age and gender but that is just an estimate. Each one of us has a difference max HR. To get accurate you need to do a field test. I think roadbikerider.com had one. Sally Edwards has them. Every coach who works with an HRM has one. Someone will post a link.