Higher Quality WebM options?

In experimenting with WebM, in comparison to H.264 with same data rate, the WebM is VERY low quality and the filesize is less than half of the size of the H.264 output at same data rate.

does anybody know any good render profiles for WebM to create a high quality output. I know it's not the codec, because, the difference from H.264 is not slight. I'm talking noticeable square boxes wherever there is lot of color gradient.

i would think that the filesize would be bigger as well for 12000k

anyways, any tips?