Testing them all on -9 is perhaps not a fair comparison. For example, according to http://changelog.complete.org/archives/931-how-to-think-about-compression-par

Testing them all on -9 is perhaps not a fair comparison. For example, according to http://changelog.complete.org/archives/931-how-to-think-about-compression-part-2 http://changelog.complete.org/archives/931-how-to-think-abou..., gzip -9 saved a tiny amount of space compared to gzip's default, but took significantly longer.