Do I really need carbon soles, or are nylon soles good enough?

Nylon soles are perfectly adequate for recreational riders and those who ride at moderate intensities. Carbon soles become worthwhile when you're riding at higher power outputs, racing, or doing long rides where efficiency matters. The stiffness difference is noticeable during sprints and hard climbing. If budget is a concern, carbon-reinforced nylon offers a good middle ground with most of the stiffness benefits at lower cost.