Higher quality lenses also require a higher quality review(er). Just putting it on your camera and going outside and shooting some objects and posting centre crops doesn't cut it.
That's true of all lenses, of course. But I don't think test chart comparisons are terribly helpful either. What I would rather see - and which Brian will surely do when his review shows up; it's one of the most useful aspects of his reviews - is comparisons of photos of actual subjects of various sorts: portraits, buildings, landscapes, etc.
I suspect the Sigma will prove to be a superb lens, and wouldn't be at all surprised if in may ways it beats the 50L - though if I used a 50mm lens to take portraits I would be far more interested in which has better bokeh than which shows the most clinical detail.
(Personally, I have no stake in this particular debate - if I want crazy sharpness from a 50mm-ish lens, I suspect that my Sony/Zeiss 55mm 1.8/Sony A7r combination is at least as sharp as the Sigma would be on any current Canon body, while weighing less than the Sigma lens alone, and if I want a blur-fest from a 50mm-ish lens I'll use my manual Canon 55mm 1.2 on the Sony.)