Upload & Sell: Off
The reason I buy Zeiss ZF lenses is not for their overall optical performance. Each and every one of the lenses I own (21, 28, 35/1.4, 50, 50MP, 85, 100MP) has its own fairly serious optical shortcoming. The reason I buy them is for the look, that special look, which I rarely see from lenses other than Leica, Zeiss and Schneider-Kreuznach. Olympus has a few really good lenses though, especially the 12/2, which, while good, isn't perfect, yet I keep coming back to it, and it is my most used MFT lens by far.
The special property of the Zeiss lenses is that sense of being there, a special clarity and transparency, combined with interesting boke. Leica lenses don't have that, but they have gorgeous, painterly rendering, without sacrificing sharpness. Schneider lenses are somewhere in between.
I own the Sigma 50/1.4, and it is a really nice lens, but it doesn't get so sharp stopped down, and the look wide open, while beautiful, is also somewhat lacking in character and colour. I don't think I will sell it, but I don't hold it in the same high esteem. I imagine that the 35/1.4 will be better, but that my emotions would remain those of detachment. Still, it sounds very good and I am keeping a careful eye on it.