The kinetic energy goes to infinity as the speed of a particle approaches the speed of light, so there's no upper bound on the kinetic energy a particle can have in special relativity. The formula you possibly had in mind, mv^2/2, is valid only for v much less than c; for relativistic velocities the energy of a particle is equal to mc^2/sqrt(1 - v^2/c^2).
BTW, it's any kinetic energy that contributes to the temperature, not necessarily vibrational.