Depends on the type of runner that you are - a true 400/800 guy (like Rudisha) is better off with that positive split. Hoppel is NOT a 400/800 runner, nor was Symmonds, and certainly not Kessler (obviously). Arop is more on the 400/800 side although has good endurance (but not great - or he would be running 1500's), as seen by his 1k (2.14) races. Korir (whose career seems to be in decline) had the speed to run 1.40 (44.2 400m), but never or at least rarely ran for time - but won an OG title.