Sorry, I thought I had mentioned the user count. It is a small install with only 4 users. Each has their own library and their own camera uploads library, and there are also 3 shared libraries that are shared among the users. Encryption and history are enabled on all but the camera uploads libraries. Total data is around 35GB. There are 6 connected computers and 5 connected mobile devices. Two of the shared libraries are the most actively used so when there are changes in those they sync to three or four devices at the same time. But that would be the max concurrent.
I do not know how far it could scale, but as I mentioned I also have CrashPlan running on the box which is a bit of a cpu and iops hog when it runs its data compaction and cleanup (about 3 hours daily and once a week for about 6 hours). Even when that is running I see no issues with my Seafile instance.
The server is running Ubuntu 14.04 with Seafile 6.07, but I have been running this server since 4.3.2. I am also using the apache method to proxy the web traffic to enable SSL (with seahub fastcgi).
Not exactly the answers you were asking for, but that is what I know and can offer.