BTW my system is as smooth as FSX could ever be. It will *Never* run this smooth with three open views on one PC; and the VAS...
With a single view, you will add to the smoothness, the elimination of any possible network lags and a modern video card has the ability to run 3 views with the same fps, it only depends how you play with settings like antialiasing, for example, which have an effect on fill-rate. On top of that, even you managed to convince all 3rd party add-on developers to support network connections, every additional add-on that did that, would increase the network traffic, increasing the chance of lagging or micro-stuttering due to the network sync process so, the more add-on supports this, the more chances they could slow down the network.
And it's not just something you can solve with faster network cards/switches, it's the very process of each add-on client having to synchronize its internal state with the one of its server AFTER it has received a packet, that adds to the workload.
Suppose you have a complex 3rd party add-on with hundreds internal variables to transmit: they first must be transmitted over the network, and then the client would have to update all those internal variables so they match those of the server. Doing it twice, because with 3 screen, you have 1 server with 2 clients. Do it at every frame, of course, because if the add-on does something *visual* like GSX, it must be updated at every frame. Multiply with the number of add-ons that do this.
If the clients would do it immediately in one frame, you would see micro-pauses. If the client tried to eliminate micro-pauses by not trying to updated everything in one frame, you would see lagging between servers and clients. Not a problem if you are updating instrumentation data, but immediately visible if you are updating scenery stuff.
Speaking about VAS, if you run FSX in DX10 or Prepar3D, there's no difference whatsoever in the used VAS between using a single screen or many, this would be an issue in DX9 only, and almost all our products, including of course GSX, are fully compatible with DX10 and they are all compatible with P3D too.