If you have not noticed, a new version of the web API is now in place.
The new version comes with a lot of improvements out of the box.
First, /streamzip has been redone. You should expect streamzip to be more performant than the previous versions.
We added more concurrency to the whole process which should speed things a bit, and also redid a lot of the code to use some newer aspects of AWS S3 SDK.
As long as your biggest file is not bigger than 100GB, you should have no problems using this service.