First, you have no idea which man in his prime would have run faster in a 5K or 10K time trial under similar conditions. If Bekele had been the man of the 90s, and Geb had been the man of the 2000s, their PRs might well be reversed. That's just the way things work when people are chasing world records and racing against the competition of their own era.
Second, the fact that Haile could run under 27 last year is hardly a good reason to think that he couldn't have beaten Bekele when he was in his peak years on the track a dozen years ago. Quite the opposite. It suggests that Haile probably could have run significantly faster at his peak if he had been pursuing faster records and racing faster competitors.
Third, I'm not sure what you mean by "a world beating situation," but it sounds as though you mean a rabbitted race that's designed to produce fast times. To me, that's not "a world beating situation"; it's just a lab experiment. To me, "a world beating situation" would involve putting the world's best runners on the track, each man trying to beat everyone else, with no rabbits or domestiques to assist anyone. I think that Haile in his prime might very well beat Bekele and everyone else in that race.
I don't say any of this because I'm a big fan of Geb, or because I dislike Bekele. In fact, I was always on the side of Tergat against Geb, and my admiration for Geb has diminished a bit during his string of paced road racing exhibitions in recent times. Conversely, I hated to see Bekele get blown away in the 5K Olympic finals in 2004, and I've been super-impressed by his cross-country running, which makes me somewhat inclined to say that he's the best distance runner ever. But 10,000 meters on the track against Geb in his prime, in a real race with no rabbits, is another matter.