The engine displacement alone, such as 600cc or 650cc, is not the sole determining factor in a motorcycle's speed. There are various other factors that affect the speed and performance of a bike, including engine design, power output, weight, aerodynamics, gearing, and rider skill.
In general, comparing a 600cc bike to a 650cc bike, it is not necessarily true that one will always be faster than the other. The specific model, make, and design of the motorcycle will have a more significant impact on its speed and performance. Two bikes from different manufacturers with the same engine displacement can have different power outputs, torque curves, and overall performance characteristics.
Additionally, the intended purpose of the bike can influence its speed capabilities. Some 600cc bikes are designed for high-performance sport riding and may have more aggressive engine tuning and aerodynamic features, making them capable of higher top speeds. On the other hand, certain 650cc bikes, often classified as middleweight or adventure bikes, may prioritize torque and versatility over outright top speed.
Ultimately, it is important to consider a motorcycle's overall design, engine specifications, and intended purpose rather than solely relying on engine displacement to determine its speed potential. If you are interested in a specific model, it is advisable to consult the manufacturer's specifications or review performance tests and reviews to gain a better understanding of the bike's speed capabilities.