Bekele is Bekele. You shouldn't bet against someone who's run 12:37.
Lagat is great, but I think he would probably be beaten in Osaka. His slowing down on the speed end, its obvious, all of his 15's have been slower than his usual self. He's been lucky to close under 42 300 in quite a few races, (USATF, Paris) Reebok was his fatest off a very slow pace at 41.8 I believe.
Meanwhile, Bekele is speeding up on the speed end, having run 3:50 or its equivalent on numerous occasions and displaying a 53 final 400 in a 3k already. Bekele could at least hold him off with a 52-54 last lap on a 13:0x pace. The big ? is could Bekele hold off Mottram who could also run a 52-54 final 400 off the same pace, and a good number of Kenyans who consistently dominate 5k's with finishes in the same range.
Bekele has no fear of Lagat, but he seems to fear Mottram as does Tariku. Lagat has a better shot in the 5 clearly, but its still not that great when you look around him. He should run both to see if he can try the same thing in Beijing. If not, he should just run the 5k, and maybe a few 15's or miles to keep his fast gear up (which is still blazing fast btw).