I agree Robert. He will run low 47's maybe a high 46's because it is a training exercise.
Instead of doing 6x400, he's doing 1x400 as a time trial to see what he needs to do for the 200m races he plans to include in his agenda this season.
My quarter milers used to run 3x800 under 2:30 with equal rest at the start of the season. If not I'd run them in 1x800 at a track meet to see what type of LAT work I'd have to design for the next few cycles.
I like the analysis you offered to arrive at your prediction.
At the upper end of your scale, it is possible for Asafa to run in the 43 range depending on how well he can adapt those fast twitch "B" fibres to process oxygen for recovery while running.
He has Type IIB, MJ has Type IIA, they're similar but IIA is more oxygen tolerant.

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