I've been having a lot of fun shooting large panoramas with the a7R and thought I'd share some of my experiences.
First, be warned that 650 megapixel images can be addictive.
I originally bought a Gigapan Epic 100 (on a friend's recommendation). It's an automated pan head that greatly simplifies shooting multi-row and multi-column pans. But it's not really big enough to adequately handle the a7, the trigger device seems to cause camera movement sometimes, and the included software is rather weak. So I sent that back and planned to buy the larger and much more expensive Gigapan Epic Pro. Unhappily, even after I came to grips with the price, I learned that it doesn't yet support triggering the a7 (due to the new 'multi terminal' connector that Sony has switched to.)
But I was hooked on these big images, so I went hunting for another solution.
I came across a nifty little product called the Panosaurus. Unlike the Gigapan, it's a manual pan head; but it is nicely made, quite sturdy and only $100. While I was waiting for that to arrive, I also discovered a fantastic stitching software called Autopano Giga, which puts the Gigapan software to shame.
Still have a lot to learn about the best techniques (choosing focus points in a big pan, exposure considerations, etc) but it's a blast to be able to create these mega images so easily. Now that I've seen the possibilities, I will probably end up ordering the big Gigapan and hacking a shutter release cable myself so I can use it with the Sony.
Here's a shot of the Minneapolis skyline, stitched from 34 shots. Shot with the 70-200mm zoom at 200mm. The full-size pan is 61,689 pixels by 10,568 pixels (652 megapixesls). Here's a link to a slightly reduced 30,000 pixel wide version in case you'd like to look closely.
Below are some random 100% crops from the image.