Cannondale SuperSix Evo kids bike

RS81-C50 is wider, and has tartier hubs, than RS80, plus it is 11s compatible so more future proof. On the other hand, they are £90 more than Zipp 30s and I'd put money on the Zipps being faster.

I would go for the Shimano's personally. I ride with someone who has a set of those Zipps twice a week and they have been nothing but trouble (though he's reluctant to admit that). They make a nice noise though.... when the skewers aren't creaking loud enough to drown out the wheels.