if you check out this old sports illustrated article, you'll see that pre had bests of:
100: 10.7
200: 23
400: 49
http://sportsillustrated.cnn.com/vault/cover/featured/8182/index.htm
(go to page 31)
based off the low end, i'd actually think he could muster a faster 400.
is this really relevant, well, hardly. just because pre could run 49, doesn't mean bekele can of course, but really, seriously, the guy can, i am sure, run just around 49 flat. i agree about the limited variation in stride length against the variable of max turnover.
hell, even my own fastest recorded 400 is 54 high(relay), but without any further specific training i'm sure i could have mustered a 53, it's just that, as a two-miler, i didn't have the need to step down and do it.