The 300 series, has no, or almost zero carbon content, and won't benefit by heat treating. It is also rather gummy to machine.
The 416, has carbon, and can be heat treated. the benefits are, a supposed higher resistance to rust, although you couldn't prove it by me. It is easier to machine, it is VASTLY easier to solder than the 300 series.
When heat treated, 416 only gets to the RC30s, I believe.