Water flow is very important as important or more than psi. Cat pumps are the best, there are many other pumps that are good too. A Honda gx390 engine on a 4gpm and 3600psi pump or higher is ideal. Here’s a Yamaha unit that’s a excellent buy.
http://www.performancetoolcenter.co...V8rCL3AIVymSGCh2GRAPYEAQYASABEgJ3iPD_BwE

I have a Honda gx390 engine with a comet 4gpm, 4000psi pump. It will get any job done you want done and get it done much faster than a lower end unit. You can always adjust your pump pressure back if your cleaning something delicate, it only takes a second to do it.