PSI & mighty m12

I am a portable using cc guy, new to the business and am wandering about proper psi. I have a 500 psi machine currently and am wanting to add the mighty m12, 1200 psi machine so I can do t&G. it is 1200 psi or 250 psi (not adjustable) and was wandering is 250 psi enough for carpet cleaning and is the mighty a good machine for the $. And if 250 psi is enough to do a good job on carpet, why are people buying 500 psi machines. WOuld likr to carry the m12 on my van and use my current porty as backup. my van is pretty full now.

low pressure = low moisture??