i've been struggling with my next lens purchase and i've narrowed it down to the 24-70ii and this sigma 1.4. clearly, price is not the issue - space in my bag is! i like to pack light, and i love 35mm. the question: do you guys believe the 24-70ii will outperform the sigma 35 at 35 f/2.8? i generally prefer primes due to size/weight but everyone can't stop talking about how great the 24-70ii is, and i don't often shoot in low light but man, if i get this sigma i might just have to!
extra, relevant info: i own the 24-105L
i plan on making the purchase after canon's apr23rd announcement - i know it's a long shot but i've been waiting for a 35mm 1.4ii from canon for a long time - what say you canonrumors? thank you in advance for your help 
Man, tough comparison. The 24-70 f/2.8 L II is not a light lens at all, it's optically incredible, with the price to match as you know. I could see you selling the 24-105 after getting it though, you won't miss the extra reach with the quality of image coming from the 24-70.
While I didn't do side by side tests, I do have some shots taken at 35mm on the 24-70 and they're pretty much perfect... so can the Sigma out-perform the Canon? No, I can't say that it would. But then, I'm not using the Sigma at 2.8... I'm using it at 1.8 - 2.2
The Sigma also isn't a light lens, though not as hefty as the Canon 24-70. If price isn't an issue I'd say go with the zoom, you'll get a lot of use out of it. But I, personally, find a lot more joy out of using the Sigma... hope that helps.