Below are some notable 400m/1500m PB combinations I found. So again, one wonders, will Rudisha break 3:40 in the 1500m (with a 45"50 400m PB)?
André Bucher (SUI)
46"32
3'38"44
Hezekiél Sepeng (RSA)
46"50
3'38"24
Sebastian Coe (GBR):
46"87
3'29"77
Wilson Kipketer (DEN)
48"00
3'43"29 pace in Mile PB = 3'59"57
Note: Kipketer had 75 races under 1'45"00, and Steve Scott (USA) never eclipsed that (800m PB = 1'45"05), while his mile PB is 3'47"69.
Alberto Juantorena (CUB)
44"26
3'45"5
Yuriy Borzakovskiy (RUS)
45"84
3'40"28
Steve Ovett (GBR)
47"5
3'30"77
Nick Symmonds
47"45
3'34"55
Vebjørn Rodal (NOR)
47"28
3'37"57
Mbulaeni Mulaudzi (RSA)
47"20
3'38"5h
"eldrick" commented on El Guerrouj: "at his 3'26 peak, best estimates i could get were with a 47.5 - 48s time"
http://www.trackandfieldnews.com/discussion/viewtopic.php?p=115771