Thanks for the input. Next time I'm in the vicinity of B&H, I'll see if I could exchange, although Metabones IV sells off like hotcakes and there's no guarantee there would be one in stock to try out and exchange. Or I could perhaps ask them to send exchange prior to returning.
In the meantime, this evening's test shots:
5DIII brings better quality images out of this lens, IMO. Edges and corners are softer than with 5DIII. Center is crazy sharp. Decent contrast in an otherwise flat light.
A7R + 16-35 f/4L IS
Same observation as previous. It could be the "loose" adapter. There is, after all, one added variable in the form of an adapter. This was shot on a tabletop tripod.
A7R + TS-E 90mm f/2.8
Focus peaking is amazing. Takes the guesswork out of focusing when only screen available is the on-camera LCD. Question: which setting is more useful; Peaking low, medium or high? I think Eddie may have asked this question recently - is there a way to magnify a specific area during focusing, like the magnifying glass button on 5DIII during live view shooting that enables 5X and 10X views?
A7R + TS-E 90mm f/2.8
In some of the test shots by others, I noticed A7R's ability to capture "materiality," perhaps owing to its sensor resolution? I am happy with how it rendered the glass with condensation. I think the true test for the camera in my case would be how it fares with TS-E 24II and 17. I'll see if I can do something with those combinations tomorrow...