Has anyone ever used high performance 50cc cylinders?

As title, just wondering if anyone has tried any of the tuning cylinders in standard bore size. Im assuming the likes of the polini evo 50 and stage6 racing 50 to be completely gutless out of the powerband. How do they stand up against the likes of an iron sports 70cc top end?

What sort of exhausts do people run with them? Will most performance pipes not be too fat in the belly to work with them?

I guess a 19 or 21mm carb is good enough to feed one properly.