The first part, "could the galactic cluster orbit another at 10000000km/h". Is no. For simple observational reasons. If the local group were in orbit, we would be able to see and measure the supercluster which we were orbiting. We don't see it so it isn't there.
I take it that you hypothesise that the 28% of the mass of the universe that is not visible, is in fact the moving mass of the galaxies. That is not the case. Dark matter is not the moving mass of visible matter.
First remember that velocity is a relative concept, and when specifying it, you must give a frame of reference. The relativistic mass of an object is dependent on the frame of reference. For clarity lets agree to use the frame of reference co-moving with our galaxy (which is very nearly inertial)
Our own Milky way has an excess of mass. Since we are in the Milky Way, we are not moving relative to it, there is low relative velocity, low moving mass.
The first observation of dark matter was in the rotation rates of spiral galaxies. There is a missing mass in the galaxy in its own frame of reference, and in its frame of reference. Thus the missing mass is not relativistic mass.
There is a "real" missing rest mass in the universe, probably supplied by a weakly interacting massive particle.