I don’t think the rolling cache speeds up loading stuff. What I understood from watching the last dev stream, the rolling cache holds onto stuff you’ve downloaded so it doesn’t have to download that again. Unless something changes in what you have downloaded, then it will grab those files again. If you’ve got a high speed connection, you might not notice any speed difference between streaming and pulling from the cache.
I wonder if the files in the rolling cache are compressed still, as they might be for saving bandwidth while streaming.
Since they are calling it a cache, it suggests that the game pulls the files from there and loads it into the space used during play. Possibly memory.
As far as a recommended size, I set mine to 32GB. I’ve got Google Fiber and have a wired connection for my Xbox, so I think that should be sufficient for me. If you’ve got a monthly download limit and routinely fly in the same area, having a larger cache can help keep you flying.
Once we get the ability to download aircraft, having a larger cache can be nice if you like flying a bunch of different aircraft.
Remember you can easily make the rolling cache bigger, but if you want to make it smaller you’ve got to go into the Xbox Manage Game & Addons settings and delete the big file there. Then on the next load into the game it defaults back to 16GB.