It is possible to get a carpet clean perfectly well with only 130 psi. I really notice the difference in when I use less psi. I generally use between 350 and 400 psi for 95% of carpet and only turn the pressure down when doing stairs as I find anything more than 250 psi leaves ruts in some wool with my stair tool.
Isn't it all about how much power you really need? A bit like a car, I like a car with a bit of poke but 99% of the time I don't use any more power than the road conditions and laws will allow me.
With a carpet cleaning machine you need enough vacuum to suck the water out of the carpet, If your Simon Gerard and you are cleaning cruise ships with 1000 ft hose runs you will need a Titan 875, If you are a domestic carpet cleaner using hose runs up to 100 ft you need a couple of vac motors.
If you are using massive hose runs you need nuclear heat so it's still hot at the other end, If you are using up to 100ft an in tank heater or a inline heater are fine.
If you are cleaning hard floors with a spinner you need 1000 psi, if you are only cleaning carpet a 400 psi pump is fine.
Just like cars, more power will get you there quicker. But do the everyday constraints we work with really merit spending more on having huge amounts of power?