Excellent find Mike, if this gets integrated the "Network Bubble" would hugely improve performance. I'm shocked this hasn't been part of Arma from day 1.
In terms of our own server - I often monitor server performance when I'm online. To be honest, with the specs we're running, we can't possibly get much more of a higher-grade server. 32GB RAM and an i7 Haswell on a 100Mbit line alone pretty much rules out hardware being the issue.
Also, what mission was this other server running? A high number of players has far less of an effect on performance than a high number of AI. Was the server running any mods, or purely vanilla?
The issue is almost definately a combination of BI's network optimisation, mods, mission design, and client-side settings. Like you said - go on any other server that is strictly vanilla only and you will always get higher frames. On top of that, AI numbers are obviously a huge factor in client FPS, even if the server is running at high frames.
We aren't the only ones with this issue. In fact, almost everyone in the Arma community is having the same problem at the moment. Arma 3's current MP state is not in a good way, we just have to wait until BI get themselves in gear and start sorting this out. Read the first post on this page (in fact, the whole thread from page 1 is worth reading):
Multiplayer not in playable stateIt looks like this network bubble might be our only hope at the moment.
P.S
Just as a test, perhaps we should run our private server purely vanilla only, with the same mission, allow around 10 or so players to join, and monitor what sort of performance we get.