50/1.8 is better, but you'll be disappointed unless you shoot it at f/2.8 or smaller, so you aren't gaining much. It's also not too good when focusing on moving subjects, due to the nature of the AF motor (very buzzy, very imprecise: overshoot by a bunch, undershoot by a tad, overshoot by a bit, undershoot by a hair, finally get it right; almost as though it has just one speed and the AF logic isn't comfortable with that).
My biggest advice is don't buy the wrong lens. Google for Roger Cicala's blog post "Lenses: Don't Buy The Whole Set" and enjoy the laughs plus the learning.
Remember that with wide aperture, you'll end up with thin depth of focus, so accuracy in focusing becomes more important than before. Also, although "it's all about the lens", you could be in territory where the ISO capabilities of your camera are simply a limiting factor. (I say this because you can essentially only get three stops faster than your 24-105L by renting the out-of-production 50/1.0L. After that, the only option is a camera that can go to a higher ISO, though you could purposefully underexpose the shot and raise it up in post, albeit with a high likelihood of extra noise.)





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