I hope someone will answer your specific question. The Beryl is certainly more powerful than the Slate (2 cores, USB3) and the USB port could very well power a portable USB drive. But if you are otherwise happy with the Slate you might think about something like a Pi to be your server. (When they are back in stock).
I think running a router as a server is something of a party trick. It can be done but a router is engineered to do one thing.