[wrycoder]

There is currently no way to differentiate between Einsteinian relativity and Lorentzian relativity. The latter proposes an absolute reference frame. The CMB frame would be a reasonable choice for a stationary structure at the Planckian level that would host the energy bundles (quarks etc) that make up objective reality, cf. loop quantum gravity.

A one-way measurement of the speed of light is needed to differentiate between the two theories, and that has not been accomplished. In fact, it may not be possible in principle to do so. Choice then becomes a matter of taste and philosophical/physical economy.