In continuation of a previous work, numerical results are presented, concerning relativistically counterstreaming plasmas. Here, the relativistic mixed mode instability evolves through and beyond the linear saturation, well into the nonlinear regime. Besides confirming earlier findings that wave power initially peaks on the mixed mode branch, it is observed that during late time evolution, wave power is transferred to other wave numbers. It is argued that the isotropization of power in wavenumber space may be a consequence of weak turbulence. Further, some modifications to the ideal weak turbulence limit is observed. Development of almost isotropic predominantly electrostatic-partially electromagnetic-turbulent spectra holds relevance when considering the spectral emission signatures of the plasma, namely, bremsstrahlung-partially magnetobremsstrahlung (synchrotron radiation and jitter radiation)-from relativistic shocks in astrophysical jets and from shocks in gamma-ray bursts and active galactic nuclei.