50mm lowlight prime for 7D

Hi everybody, I am currently thinking about buying a 50mm prime for taking the pictures of my kids: I am using the Sigma 30/1.4 for most of my indoor pictures. However, as my kids grow, I am starting to take more and more pictures from e.g. kindergarden, the 30mm start to be a bit too short for this action. I borrowed a C85mm/1.8, this seems to be a bit long. So 50mm is an obvious choice...

What I am looking for:

- of course great IQ wide open (99 percent shall be indoor lowlight photos at 1.4 - I don't care about image quality at f8...)

- fast (and accurate) focusing to get the action

- aperture 1.4

The obvious candidates are Canon 50/F1.4 and Sigma 50/F1.4. There are quite a few reviews comparing them, however, the results vary completely: some reviews praise the Sigma saying Canon is almost unusable wide open, the others say that Canon is as good as Sigma, but cheaper with faster and more accurate autofocus...

Which lens do you guys think shall be better for my use?

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Canon 7d + Canon 10-22 + Tamron 17-50/2.8 + Sigma 30/1.4 + Canon 60/2.8 + Tamron 70-300