The Sigma is an absolute stunner. Both on the Olympus E-30 and the E-M1 is the sharpest lens in my lens Park (and there are with the 50-200 SWD and the 14-54 Zuiko lenses really good at the start) and also has a lot in Crops good reserves. The AF function properly, quickly and accurately - even in conjunction with the MMF-1 at the E-M1.
There are simply no comparable long macro lens for FT or MFT. And when imaging power it needs is by no means behind a 50 Zuiko or the newer 60 Zuiko macro lens hide.
And all diehards macro photographers who think good macros are only possible with manual AF, I invite gladly on the brand-related Oly - a platform. There there bearing this Nick a lot to see ... ;-)
VG
Verdeboreale