Well, yeah, that's the thing though, I for one am trying to fit it on a disc, so, the bitrate and the size aren't really the variable quantity here, it's the resulting video quality, because ideally, the final mkv file will be 4.37 GB (or maybe 2.18 to fit 2 films on a DVD5 or 2.6 to fit 3 films on one DVD9 but the file size should always be fixed) and if the resolution is higher, you'll get more compression artefacts at the same file size.

But I totally see your point, it's just that I don't take x264 mkv as a way to not need discs, it's a way to have better quality on the disc of the same size.