Managed to build a relatively fast (as fast a the hexagonal filter of same size) separable disc shaped filter.
I put a small demo together showing the hex and disc filter in action:

Demo Download

The different kernels of the filter passes:

It requires one more pass with one more sample than the hex version to blur out the resulting pattern, but the hex filter requires one additional RT.

Last edited by Hummel; 02/14/12 00:02.