I can answer this as I run 20 MPW per week (usually 4-6 miles easy three or four times per week): 20:30 for the 5K, about 5:45 for the mile. I have no problems breaking 20 MPH easily in sprints.
I'm random athletic guy in my early 30s. I never ran track or cross country in school (my biggest regret), but would always be either the best or second best at the PACER test in my P.E. classes, and I always beat a classmate who ended up running 18:00 for a cross-country 5K in high school.
I've never broken 47 minutes in the 10K. Apparently mileage really is necessary to fully develop the aerobic systems. Go figure.