I was seriously considering getting the sigma 35 but at around $800 or so... I can't bring myself to pay retail. I did have an offer on the table for $900 for a used Canon 35mmL but I read enough about the sigma that I simply had to go that route.
Then I realized that 35mm on a full frame is like a 22mm on a crop (I'm just starting to make the transition). And I rarely ever shoot anything at 22mm on a crop... so I'm back to needing a good low light lens f/1.4 that is sharp wide open... which eliminates the 50's. So I guess my other option is the 85mm... but I have a 70-200 mkii which seems redundant... which is also why I'm selling my 100mm L and why I have all but stopped wanting a 135mm f/2.
So there we go... I want a 50mm that doesn't exist.
My Voigtlander 58mm Nokton SLii is sharp wide open on my 6D. However, it is a manual lens. There are plenty on here who will slam the lens because it is a manual, and because it's not a Canon...but I'm sorry, it is sharper than both Canon 50mm 1.4 and 1.2. Period...it just is. I bought it for around $450 from Adorama in 2011. It is a Nikon mount, but I bought the Fotodiox chipped adapter for $35...works very well (after some tightening)...focus confirmation is accurate.
The color, contrast, build quality, and focus ring feel, are almost identical to Zeiss. The sharpness is almost up to that of the Zeiss 50mm f/2 Makro Planar...from the tests I have seen. The vignetting is minimal for an f/1.4 lens on my 6D, and non-existent on a crop body. This is comparing my particular copy...I have no idea about sample variation.
I was convinced to buy the lens after looking at the test charts that photozone.de did. You can compare the results they got with both Canon 50's.
However, if you expect razor sharp focus accuracy at f/1.4 from this Voigtlander, without magnified live view, you will probably never get it. Also, if you shoot at slower apertures than near wide open, the light meter on your camera won't be as accurate.
These are all tradeoffs I'm happy with, considering the color, sharpness, build quality, and price.
One final caveat...If I were an event shooter who only used the lens for that, and had to focus and re-focus hundreds of times over a short period of time...I would just pick a 24-70 f/2.8 zoom (probably the Tamron)...and run with that.
It's a shame you don't want the 135 f2L. It has been my favorite lens for over 4 years. But the Voigtlander's color is better, its contrast identical, its sharpness on par...while it has slightly more CA, and its bokeh is not as smooth as the 135's. But then nothing I've tried beat the 135's overall bokeh (including the 200 f/2 and 85 f/1.2)...other than perhaps a Zeiss 100 f/2 Makro Planar. But then it's also a mostly manual lens that costs twice what the 135L costs...and it was overall not as grand as the 135.