When the synchronization of large file sync_gateway performance?

I saw the performance of sync_gateway description on http://developer.couchbase.com/documentation/mobile/1.1.0/develop/guides/sync-gateway/deployment/in-production/index.html, wanted to know how the performance when synchronizing large files? I use gateload test, the MinSize 10K, the MaxSize 5M in DocSize, using nginx load balancing to two sync_gateway, (each quad-core/8GB), found very low performance, want to know why?5K concurrent users DocSize in official documents is how much?

It’s expected to see some performance degradation as document sizes increase. For the 5K concurrent users - is that 2.5K pushers/2.5K pullers?