43 second guys that cruise 44 and 45 in heats have 50 meters more left in them.
so MJ could run 44 mid pace to 450 or 470 meters.
from a physical point of view, 400 guys sprint the first 200m in 21 ish, then glide sprint to the 300m mark, at which time they are under water and running backwards. some 100 m specialist guys are under water at 170m even. after they try the 4 a couple of times - they won't touch it.
the best 400m runners learn to run under water for the last 70 or so meters. moving to the 800m now they have to run about a full lap under water. without the aerobic component, no one can do that.
i see no evidence that MJ had a good aerobic component.
so without someone reporting that MJ did a great set of 600m repeats or something like that - further speculation is pointless.
with EPO you can get a 200m guy going 400m just like that.
and you can increasing his volume a lot, while decreasing recovery times. with even more advantage in heats where non users just can't recover like the user.
i don't believe anyone has cracked 44 flat without epo type ped. as for the 800 i think there were several 141's clean.