The time of the last 800m was not exactly under 1'57". These are the official timing for the last 700m of the top 4 :
Genzebe 1'42"44 (57"22 + 45"22)
Faith 1'42"88 (56"97 + 45"91)
Sifan 1'42"48 (56"63 + 45"85)
Dawit 1'43"79 (56"83 + 46"96)
According the splits taken by Jama, Genzebe ran the 100m in the turn between 700m and 800m in 15"2 and, giving a similar time for all the leading Group, we can have these final 800m :
Genzebe 1'57"6
Faith 1'58"
Sifan 1'57"7
Dawit 1'59"
Personally, I'm more impressed by the last 800m of the 3 Young athletes following Genzebe. Among these 3, only Sifan Hassan tried sometimes a good 800m (she has a PB of 1'59"46), while Faith ran, 2 years ago, in a local Kenyan race, in 2'02"8.
Two considerations :
1) I don't understand the passive tactic chosen by Jenny Simpson and Rowbury. They can have good finals when the race is very fast only, and need to understand that, at the moment, this event is absolutely NOT comparable with the same event, 2 years ago. All the new African (including in the Group Sifan Hassan, who lives from 15 years in Nederland and started there her athletic activity) are by far very much stronger than the athletes running two years ago, especially are very much faster in shorter distances. To accepet a competition of 800m with 700m warm-up is for all the athletes who were able to run this year under 4' in fast races a big mistake. When athletes run in this way, can be for two opposite reasons only : or they FEAR the race, and start already beated, or they have the PRESUMPTION to be stronger than what they really are. In both the cases, with this mentality they can't be competitive at the level of big Championships
2) In the normal culture of Etiopia, and African generally, athletesd running 800m are specialists of this distance only, and is very unusual to see athletes of 1500m running 800m in big meetings. This is more eveident for Ethiopian than for Kenyan runners, but in any case is something common.
This fact induces to wrong analysis when we look at the effective talent of the athletes.
Tirunesh and Meseret Defar ran last lap of 5000m, years ago, in the IAAF final, in 56"6 - 56"7, and is not difficult to think they could already run 3'55" also with their normal preparation, if decided to run the distance.
The big change in Genzebe is to be part of a Group including many top athletes in the World, from different Countries (coached by Jama Aden), that had mainly their focus in 800 and 1500m. This means she included a type of quality in training, never used in Ethiopia.
3) It's very funny that, with Kenya under the lens of the antidoping, are ALL the other Countries now producing slower performances, while Kenya and Ethiopia continue to win showing, with Young athletes, growing personality and best times. When people, fanatic about doping without any real info, and induced to wrong considerations by scoops made by clowns, finally can understand that the human limit for clean athletes with top talen are, by far, very much higher than the current WR, maybe also athletes with less talent can finally reach their best possible performances. Till when they don't change mentality, they are the first limit for their own improvement.
Last thing : I can anticipate that, after WCh, Genzebe will run the first 800m of her life, looking at an aggressive competion with free mind, for checking her potentiality in the distance.