The r7800 is a great router, but it maxes out around 600-650 MBit/s using swconfig (currently around 360-370 MBit/s using multi cpu-port DSA), so I really wouldn't recommend it for a 500 MBit/s WAN connection anymore (not enough headroom for the future). Yes, the out-of-tree NSS acceleration support can extend this limit, but that's a bit risky to rely upon.