Fast macro is somewhat of an oxymoron, DOF is very shallow with macros even when stopped down. A 'faster' macro is useful when you are going to use it for other shooting, portraits for example.
I have the Sigma 105, I also have a Takumar 50 and I am happy with both but they have differing suitabilities of use. The 'fastest' lens for actual macro would probably be something like the 35 LTD because the shorter the focal length the deeper the DOF should be for any given aperture although that would still be negligible in macro situations.
Of course with a 35mm you have to get that much closer to the action so it might not be practical for flying creatures.
Last edited by Damn Brit; 10-20-2009 at 07:28 PM.