cache vs. external memory

Can someone tell me what is the speed advantage (if any) of the cache over external 0 wait-state memory, such as SDRAM? I’m looking for a ‘like-for-like’ comparison of the memory access timing - discounting factors such as DMA or an external bus master delaying the external access. TIA, Warwick

Turning cache on tends to improve performance on the tcp and udp send and receive rouitenes by 20%-30%.