Visually lossless bitrate with 1-pass encoding

[codemaster]

When choosing software encoding over hardware encoding, using the x264 encoder, I know how to make the output visually lossless. I use CRF mode, with the value 15. Or I use 2-pass mode, with the maximum bitrate that CRF 15 allocates (which is 17 Mb/s for 1080p 30 fps).

The problem is that when I export a video from a NLE, I have to use hardware encoding, because software encoding is too slow. It's not just 2x slower, it can be up to 10x slower. So to export at a reasonable speed, I have to choose Intel QSV instead of 2-pass software encoding. If I choose 2-pass software encoding, and set the bitrate to 17 Mb/s for a 1080p project, I know the output file will be visually lossless. But if I choose Intel QSV and set the bitrate to 17 Mb/s, i know the output will not be visually lossless because encoding is done with only 1-pass.

So 1-pass and 17 Mb/s is lower visual quality than 2-pass and 17 Mb/s. Which means I have to set the bitrate higher than 17 Mb/s for 1-pass, to compensate. So my question is: if 1-pass and 17 Mb/s is not equivalent to 2-pass and 17 Mb/s, then how can I find out what bitrate is equivalent?

The easiest solution is to just set 17 Mb/s for 1-pass, but I was hoping there was a way to find out the visually lossless bitrate for 1-pass, just as there is a way to find it for 2-pass.