Running a 6 min/mile marathon (2:37:30) IS slow (for you), IF you can run a 2:20 marathon. And a 3hr marathon IS slow (for you) if you can run a 2:37. Its all relative to the person. But it is so obvious that:
PACING yourself correctly to the time you want to run is the best way to run a race,
that its preposterous that anyone would suggest differently.
When I was a freshman in HS one of my first practices we ran the XC course for a time. One guy went out terribly hard the first 800meters, he then slowed down tremendously and almost walked. He kept looking back and when we got within 100 meters he went hard again for about 500 meters. We again got within about 100 meters and he again sprinted. And for a bit I thought "Oh, no, maybe I am doing this all wrong, this guy is in the lead and he is taking breaks, maybe that is easier!" Well as everyone who is reading this can probably predict we slowly got closer and finally passed the guy while he was walking, quite degectedly. He tried this "technique" a few more times and failed each time. Then he quit the team.
THE END.