You don't need 47 speed to run 1:53. Krato was 100% speed based, therefore her true potential in the 800m was untapped, as she lacked strength to go faster.(quote)
K was not "100% speed based", as the 800 is still an aerobic event. It is not won by sprinters. K was also a tremendously strong runner, as both her build and finish demonstrated. She was probably the female equivalent of a Juantorena.
The only qualification I might add is that I don't think a runner would need to be as fast as she was over the 400 to beat her 800 time, but I do think that runner would need to be at least capable of 49-low - and, sadly, likely juiced.