Of course and that's not due to 64-bit vs. 32-bit but those Marvell SoCs being made for this specific use case while almost all the other SoCs on usual SBC are originally made for phones, TV boxes or tablets. Check performance numbers for older Marvell Armada 38x (Dual Cortex A9) to know what to expect from Marvell 37x0 on EspressoBin: https://forum.armbian.com/index.php?/topic/3953-preview-generate-omv-images-for-sbc-with-armbian/
The best you can expect from an A20 board with Gigabit Ethernet is outlined here: http://linux-sunxi.org/Sunxi_devices_as_NAS#Influence_of_the_chosen_OS_image_on_NAS_performance
I hope you're talking about Cubieboard 3 AKA Cubietruck since Cubieboard 1 and 2 both have only Fast Ethernet so for NAS use cases you're limited here to 10 MB/s anyway and every Gigabit Ethernet equipped board will outperform your Cubieboard. And please don't think about any improvements here. Every Cubieboard that followed CB3 (Cubietruck) was a move in the wrong direction BTW (CB6 being no exception).
