I did various WAV file tests with FLAC -0, -4, and -8. Most of the time there was very little difference in file size. Maybe 500kb between -0 and -8, and very little difference between -4 & -8.
My bad, I was testing a White, Pink Noise & Brown Noise WAV files. I did some on actual music WAV's, theres a big difference between -0 & -4, but not as much between -4 & -8.