I was a little upset when honda dropped timing gears from the vfr engine. Chains are less reliable ... belts even less so. But issues of stretch and timing are irrelevant on a bicycle drive.

Fyi, the accepted horsepower-to-belt ratio for motorcycles is around 100hp for every inch of belt width. Beyond that, stretch and slipping become an issue no matter the material. Thats why sportbikes have stuck with chains.