The short answer: big feet take 90mm, small feet take 80mm

You want your wheel base (the length of your frame) to be in proportion to your foot. If you have a relative short wheel base, then you are more manoeuvrable, you accelerate faster and will prefer intermediate speeds. 

If you have relative a long wheel base, then you are more stable and les manoeuvrable. you will accelerate slower but once you get high speeds it will be easier to maintain them.