>>779612h265 with hardware acceleration (NVENC) is way faster than anything but it's not recommended if you want something with good quality, the encoder is "newish" and it's not as good as the normal h265 encoder, and vp9 would give you the same output, so you would need to try both to see which one is slightly faster for you
btw you wouldn't make a "h265 webm", since webm is the extension for vp9; for h265 you would be making an mp4, or just a clip