I’m just a bystander (with an E300 “HiFive1”, no experience on FPGA or U500) but if I’ve picked it up correctly from other conversations, I think you get a single core at 65 MHz but otherwise fully functional with MMU and FPU and can run Linux.
The production silicon later is expected to be 1.6 GHz and I think quad core.
No doubt someone from SiFive will be along with the exact details after the US weekend, if not before.