Same profile athlete that prepared both distances :
Bekele 12:37 26:17 >1'03
Geb : 12:39 26:22 > 1'04
I don't see why Cheptegei would be able to do something different.
And he won't have 6months to prepare one race again in a no championship year.
Because you left out a new variable - pacing light. The 10k was almost impossible to get the pacing right. Even Bekele's WR splits were pretty uneven from 4k onwards. Now they have the Wavelight thingy, which makes it much easier to lock on pace. And compared to Geb and Bekele, Cheptegei is also more of a strength-based runner. Doubling the 5k time + 50s is not unheard of for runners like him. Also, as you've already acknowledged, the weather wasn't perfect for his 5K WR (dew point 68C), he should be able to shave 2-3 secs with cooler weather. So let's assume the weather is good, he will "only" need to double his 5K time + around 55s to go sub-26 (incidentally, his 10k road PR is his 5K PR*2 +56s ). Anyway, it's highly unlikely he'll break 26 first time out, (Sub 26:15 would be a good goal for him), but he definitely has the potential to do it.