It may require more transistors in some places, e.g. in longer buffer chains needed to drive greater capacitances at higher frequencies, but it requires mostly bigger transistors in many places.
According to AMD, both the big core and the small core use the same RTL design, but a different physical design, i.e. they use different libraries of standard cells (optimized either for high speed or for low area and low power consumption) and different layouts in the custom parts.
According to AMD, both the big core and the small core use the same RTL design, but a different physical design, i.e. they use different libraries of standard cells (optimized either for high speed or for low area and low power consumption) and different layouts in the custom parts.