Sorry to disagree Mark. "Anything else is useless" is just not true. It's the ability of the technician that creates a good clean, the machine is just a tool. Are you saying that me and many other colleagues on these Bulletin Boards are inadequate because we have less than 300psi? I'm sure you're not. I can understand fully what you're trying to say, but it appears to have come out wrong. High spec machines perform quicker.
My advice? Buy as much power as you can, don't be affraid of second hand equipment as we tend to think of vacs and pumps as being consumables on portable machines. If buying secondhand, vet the owner, van, his attitude etc.etc. as well as the machine you're buying in order to see whether or not he was likely to have cared for it. Formal training is vital if you are to progress as a technician. And finally, marketing is essential. It's no good being the best CC in the world, with the highest spec. equipment if nobody buys your services.
Safe and happy cleaning:)
Ken