Not a Go programmer I'm guessing.

Go can be made to run much faster than C.

Especially when the legacy C code is complex and thus single threaded, Go's fabulous multicore support means you can be exploiting parallelism and finishing jobs faster, with far less effort than it would take to do it in C.

If you measure performance per developer day invested in writing the Go, Go usually wins by a wide margin.

> Go can be made to run much faster than C.

Not literally the case.

> If you measure performance per developer day invested in writing the Go, Go usually wins by a wide margin.

I can accept that performance/hour-spent is better in Go than C, but that's different from Go's performance ceiling being higher than C's. People often confuse ceilings with effort curves.