The tests were done with IS off, using a tripod.
"*The primary and obvious perk of the L is its image stabilization. All my tests were done on a tripod using a wired shutter (and often MLU). So the L's image stabilization was disengaged the entire time. But take away the tripod and the L's image stabilization really comes into play. The L's main perk over the EX is, obviously, image stabilization (and the EX's main perk over the L is price and having 50-100mm/400-500mm). I personally am a very big fan of image stabilization, so the L remains in my bag."
It may not be the exact same lens, but it's still a decent writeup, and some additional reading on the site will find the OS version reviewed: http://www.pbase.com/lightrules/bigmos
"Imaging Quality: The image quality of the new Bigmos is "GOOD". Center sharpness, even from wide open apertures, is GOOD across the focal length coverage (e.g., 150mm - 300mm - 500mm). Border performance, however, like the original Bigma, DROPS OFF and trails the center by about 1.5 - 2.0 stops before catching up. The Canon 100-400 IS performs slightly better at the borders, at least wide open. But again overall sharpness is GOOD and certainly being "only" a 3.3x zoom lens helps in its strong performance across the focal range. Contrast reproduction is VERY GOOD; greens are especially nice and pleasing. The lens does exhibit a slight warm or yellow color cast, but nothing too drastic. Light falloff is SLIGHTLY EVIDENT at wide open apertures, but quickly dissipates even one stop down. Distortions are WELL-CONTROLLED; nothing flagrant at all. Its flare performance is EXCEPTIONAL; I noticed hardly any hot spots or veil-flaring of any kind. And I never even mounted the hood! Lateral (or transverse) chromatic abberations are present wide open but again, it is not flagrant or obvious. Overall the new Bigmos is a GOOD OPTICAL PERFORMER and only slightly inferior to the 100-400 IS. **SCORE 8.5/10**"
Budget and ultimate usage would dictate which lens to go with, really. Personally, I'd prefer to get sharp shots with the "pump" and crop; but I've seen one or two folks on here that post up fantastic shots using the Bigmos.