I don't know, I have both the 40 and the Canon 50mm 1.4. Both are fairly new purchases, so I'm still excited about both which is probably a better comparison. And with that said, I like the 50 1.4 better. Now, if it was a 40 1.4, that might be different.
I like the option of using the 1.4 in lower light, and I like how you can get even less depth of field to make things pop. Sure, at 1.4 the 50 isn't as sharp, but it's still good enough if need be.
I'm definitely keeping both though, since the 40mm is so portable. If you just take 24-105 or just a 70-200 for some reason, you can always stuff the 40mm in a side pocket without bulking up the bag or increasing the weight substantially.