I'm using the A7Riii. I never use AF-C so it's not a problem. Still, I find it foucesses quickly and I would suspect that the AF-C speed will depend more on the camera. I also tend to avoid using it below f4 since that was the optimal sharpness aperture on OpticalLimits. 42 MP gives me a lot of noise control upon downsizing and the high iso results are pretty good as is. The other similar FL lenses I've used are the mu34 Panasonic 20 and the Fuji 27. Both of the latter tend to be "clinically" sharp, although it's hard to make a real comparison since I can't mount these lenses on the same body. I just really like lenses in the 40-50 mme range. The obvious competitor would be the Samyang 45 1.8, which is faster and cheaper. I looked at some reviews and prefered the look of the sigma but I wouldn't want to put my reputation behind that observation.
I think you meant AF-C, not APS-C, correct? I use a mix of both Single and Continuos focus on my A7ii, but if I had a mkiii cam, I think I’d live in AF-C for most of my shooting.
Yes, the Samyang 45mm also looks mighty temping in this focal range. Dustin Abbott seems to prefer it over the Sigma and there are a lot of happy users for that lens on the FM forum. Although Fred himself definitely praises the rendering of the Sigma very highly.
The Sigma pulls at me for it’s build, aperture ring, and compact size. Just wish it was sharper wide open and close, as that’s where I think I’d like shooting with it for snaps of the kids.