That's definitely the most beefy Single Board computer I've seen to date, especially with 4GB of RAM, should be able to run a browser at a reasonable performance.
eMMC via the ZIF connector on the Rock64 is a bit of a pain to get setup, involving a serial console and uboot commands, but I see better than 20MBps on an A1 class uSD. I use a USB3 SSD for my /home, it's even faster.