long before gmap-pedometer, people would drive routes, or bike them with an odometer, and they'd know their time at the end.

I've almost never ran with a heart rate monitor, gps and sometimes not even a watch(look at clock when I leave, look at clock when I arrive home). Yes I'm a decent runner.

You shouldn't worry about your speed, you should worry about your perceived rate of exertion and what your goal is of the day. Is it a hard day, easy day, tempo day, hill day, interval day, threshold day? Not all days should be the same. If you can run 5k comfortably at 6.7mph then....

one day a week you should run 5-5.5 mph for 5-10 miles
one day a week you should run 4 miles. Start with a one mile warm up then alternate one minute hard at 7-8mph, and two minutes easy at 4-5.5mph.
one day a week run 6 mph but every half mile do a "hill" on the treadmill for a half mile.
one-two days a week do your 5k at the comfortable pace.

I know how fast I'm running in general just because I've ran thousands of miles in my lifetime. This isn't to say I don't need a watch when I'm doing my track workouts, but I get by in training runs.