Ubiquiti maintains a fork of Vyatta (which is related to VyOS in ways I'm admittedly not quite clear on) that also has a web interface. It's for their hardware, but the EdgeRouter series is quite decent in terms of both performance and cost. (The Lite platform will do gigabit line speed for about $100.)
I've used Vyos and was generally impressed. The part where we used Vyos was not exercised to capacity. One thing that confused me was how most (all?) networking hardware of today makes use of custom ASICs (e.g. chips from Broadcom) to get line speed in routing etc. How does Vyos/Vyatta compare? If you had your VMs on the same host as the software router, I understand it is going to be really fast. But if you have a separate box, don't you see a significant slowdown?
That depends on if your network card supports TOE. If your network card supports full TCP offload then your routing latency can be as low as .6-1.4 us. If you have to go through the entire TCP software stack it's around 20-40 us, on 10Gb hardware. Full TCP offload puts it in the same ballpark a hardware router.