Women do not convert 400m speed to 800m speed equally either. Take a look at the following 400m vs 800m bests of these gals:
Jarmila Kratochvilova 47.99 1:53.28 (8.650/lap slower)
Jearl Miles-Clark 49.40 1:56.40 (8.800/lap slower)
Ana Quirot 49.61 1:54.44 (7.610/lap slower)
Maria Mutola 51.37 1:55.19 (6.225/lap slower)
Ludmila Formanova 51.84 1:56.56 (6.440/lap slower)
Stephanie Graf 52.69 1:56.64 (5.630/lap slower)
Pam Jelimo 52.78 1:54.01 (4.225/lap slower)
Meridith Valmon 53.25 1:57.04 (5.270/lap slower)
Christine Wachtel 54.36 1:55.32 (3.300/lap slower)
Jolanda Ceplak 54.67 1:55.19 (2.925/lap slower)
Maggie Vessey 53.61 1:57.84 (5.310/lap slower)
Vessey and Pam Jelimo seem not to fit as nicely into the chart. So, really how fast is Maggie in the 400? and how much would you add per lap to her 400m time? I say 52.8 and add 5.50 seconds for a nice 1:56.6
The one with the smallest variation between 400 and 800, Jolanda Ceplak, is just coming off a 2 year ban for testing positive for E.P.O..
The next one on your list with the smallest conversion factor, Wachtel, was a member of a 4x400 bronze medalist team and I sincerely doubt she ran 54+ leg on it.
Meredith Valmon (nee Rainey) ran 51.56 for the 400 while at Harvard, so that time needs adjustment.
Vessey should be able to run sub 52.00 right now or 4:02 for 1500. Obviously, the greater the 1500 speed the less 400 speed is required to hit a specific 800 time.