Total Codswallop
That's English for BS.
how much energy a given mass
can contain
As you accelerate a particle, it gains energy. Energy and mass are equivalent (E=MC^2), so it also gains mass. The closer it approaches C, the more massive it becomes. There is no theoretical limit on it's energy or mass.
In principle, if you took all the matter in the universe, and converted it to energy (except one particle) and put all that energy into one single particle, then that particle *could* be considered to have reached the highes "possible" temperature.
Why don't you just backtrack to the Big Bang - that was about the same thing.
Go and learn some physics - your "questions" are risible.