A bit irrelevant at this point, but just thinking about Ryan Hall. He obviously had success in the marathon, but he also had some dark moments in there as well. Maybe the marathon wasnt his ideal event?
In high school, he ran 1:50, 3:42(for 1500), 8:55 (for 3200). All great times, none of those suggest to me a need to move up to longer distances.
In college, he never ran a serious 800 or 1500. His 5000m collegiate pr of 13:22 was clearly better than his collegiate 10,000m pr. To me, this suggests his best event would be 5000m or shorter. I'm not sure why somebody with a better 5000m than 10,000m would decide to leap up to the marathon instead of focusing on 1500/5000m.
Was it a lack of contemporary American competition that caused him to move to the marathon? Anybody know if he's ever covered this? He has talked about how he thinks marathon training ruined his body, maybe that's because (in my view,) he was really meant for middle distances?