One solution might be to hire a pressure washer before buying and ask a company expert in the field what they recommend. Don’t forget to factor in to your costings any servicing that may be required to make sure the washer will work at optimum efficiency.
Pressure alone is not an indication of effective cleaning as water volume plays an important part. For instance high pressure used with a low water volume will produce a powerful but narrow water jet which may be ideal for cleaning small areas of ingrained dirt but not so effective for cleaning larger areas with a lot of debris to be removed. In this situation a pressure washer with a larger water volume cleans more efficiently.
To reduce uncertainty ascertain how long the washer would be used each week and how hard it would have to work. To have a washer working at full tilt all the time will not improve its longevity. It is also important to think about the kind of cleaning required is the dirt caked on? Do you want to clean large floor areas or smaller pieces of equipment. Do you need a hot or cold water version?