Size can hinder a runner in the 800 and 1500m, as you'll know if you watched Anass Essayi, who has the best pr in the 1500m field, get bounced around repeatedly. But Sumner has enough size. That is not an issue for him. He closes like a freight train. I too think that close plus 400 speed means he could be an absolute star at 800/1500m like Coe. You do not see 1500 guys very often with low 45 or sub-45 speed, but then you do not often see guys with that kind of 400 speed close really hard in the 800m regularly like he does. He has more endurance than the other 400 AND 800 guys, and his parents both ran the 800/1500 double, if I recall correctly. Still, he showed here that he has more than enough 800 talent to be a world contender. Brazier's hs 1:47 was a 2 second negative split and showed he could run 1:45. A year later he ran 1:43.55. Sumner just dropped about 2 1/4 seconds from his hs time, which was within a tenth of the hs record, and he did it with a 2 second negative split that suggests he can break 1:43 this year. He has a great future.