I returned my sigma yesterday and got my 35L today. I was extremely happy the first 15minutes. The handling is right; the AF is substantially faster (maybe 30%?) and incredibly consistent; and the bokeh is beautiful.
Then came slight disappointment. On computer screen even without zooming there's very visible CA and purple fringing on some images. I think I'm seeing them because I know where to find them.
Sharpness wise the 35L is sharp enough at 1.4. Maybe Sigma is sharper but the 35L is sharp enough for my purposes.
I love the AF and handling of the 35L. Every shot so far is accurate. The CA is a bit annoying. Maybe this is the biggest limitation of this old lens. There's less vignetting than Sigma but I care less about this. I think the 35L is too expensive also. The Sigma is priced right. But its AF is a big disappointment, at least as far as my copy is concerned.
I'm leaning towards keeping the 35L. There is quite a bit of work to remove CA in LR, but maybe I'll live with that.
Maybe I'm missing the point but I just remove CA with one button in LR. Removes enough of it to be a non issue for me at least.