VirtualGL won't help unless the application is using OpenGL. More than
likely, your bottleneck is in the encoding/transmission layer, not in
the X proxy itself.
Have you tried TurboVNC? It's a fundamentally different type of X proxy
than x2go, and it's designed for exactly the type of workload your
application is creating (displaying a stream of images in real time--
because that's essentially what VirtualGL does in an X proxy environment.)