Since the decoder complexity of flac is much lower than that of opus LossyWAV easily wins this competition at 300 kbps. I just wonder what the compression artifacts with LossyWAV would sound like if you push the bitrate down further (like e.g. 128 kbps). Sadly the command line tool does not allow that.
Would be interesting. Unlikely to work out though. On other note, opus 128 kbps is transparent (in my tests i can distinguish 100kbps files at most), with safety margin 256 kbps should be enough for all practical purposes (except archiving).
There are other worser codecs around, e.g. LDAC (best Bluetooth codec) 660kbps vs 990kbps is very noticable (cant setup the same way to compare 990kbps LDAC vs 128kbps opus)
What are you doing with it that opus decoding complexity is any kind of barrier?