1) Kenenisa has already won a major marathon. It was in Paris. It was not a "clown show" by any standard, although the field was not loaded like various other yearly marathon majors are.
2) I don't believe Kenenisa's calves or overall all body size & frame place limits on his performance at any distance. I think he is an extremely efficient runner and this likely carriers over to any distance.
3) It's foolish to assume Kenenisa is "not hungry" about winning and setting records. The man has been so hungry for so long. I'm sure he was especially hungry after not running for 11 months due to injury, because he came back and almost broke the world record in his 3rd marathon after doing so. His ambition and enjoyment of competition is evident in his smile and his body language at the finish line when he wins. He always drives 100% through the finish line as hard as he can, and is extremely tough at the end of every race. I'd say Kenenisa might be the hungriest and most ambitious runner alive.