The quarter mile thread inspired me to question which is better?? I know (as well as you do) folks who do mile repeats for 3000's, 5K's, 10K's up to the marathon. What are the benefits of 400 repeats, 800 repeats, 1,000's miles, etc. Is there a general rule of thumb?? Is one better than the other?? Seems like 5 x 1mile could substitue a 20 x 400 workout. Any thoughts?