Compression Bitrate versus ISO - noise reduction question

My default shooting is UHD/59.94 using constant bitrate with 12:1 compression.

I'm memory card constrained, and at night often light constrained. My lens is already wide open, and I'm shooting high ISO. Obviously there's a fairly large amount of noise which is not surprising.

I'm wondering whether because of the noise when at high ISO, would there be more of a benefit to lessening the compression ratio, i.e. to 8:1 when using high ISO, than there would be when using low ISO with less noise?

I'm thinking about the times when I might have enough space to shoot some (but not all) content at a lower compression ratio than others, and whether it could be sensible to pin that decision to the ISO being used - i.e. 8:1 at high ISO, and 12:1 at low ISO?

Thanks,
Roland.

Noise is enemy of the encoding and if there is a lot of it then every codec will struggle.
So noisy 8:1 can be relatively treated "the same" as quite clean 12:1. There is some truth there although values may be bit different (but you have only 8:1 and 12:1 and nothing between to choose from).