ransley wrote:

What is the minumum rating (in terms of gpm and /or psi) that
make it worth while to actually buy one of these things?

I think that is the more relavent question here.

What are you washing

Today it might be one thing.

Tommorrow it might be something else. Next year something completely
different.

Now do you see why asking "what do you want to wash" is irrelavent?

If I wanted to buy a set of wrenches, or a drill, would you be asking
"what want to assemble / disassemble?" or "what do you want to drill?".