From where do you know that the clock on this Turbostar 540+ is running too fast (i.e. that they didn't change the clock timer or the ROM)?

IMHO changing both the CPU and the IRQ freqency at the same factor wouldn't make any sense, would it?
Such an overclocked device would play exactly the same moves and games as the normal device, just everything at a higher speed - it's just as if you would increase the emulation speed in MAME by the same rate (5.53/4), so I don't think it's useful to add this 'real' model 540.