There are a lot of hoses that are rated for 250 deg and 3500 PSI. I have talked to a lot of people influential in the industry about them, and they are unanimous in the opinion that, even though they have those ratings, they are not capable of doing both at the same time. What is more, once you release the super heated water from the water, it disperses so quickly that the striking power of the water is diminished to non existent. That is why all these steam cleaners need the brushes in order to be able to remove gum, etc. The steam, released in a controlled manner, super heats the gum, and the brush releases, for a lack of a better term, the surface tension, or adhesion that is holding it on to the surface.
I remember when a contractor brought his super rig to Las Vegas, that while a little heated 4 gpm pressure washer was removing gum like most of us typically do, his rig, that purported to reach 300 degrees just couldn't get the gum to budge. If he had a brush, he probably would have been able to remove the gum as fast, or faster then the little machine, because of the scrubbing action. That is the HUGE problem that I have with pure steam cleaning anything like garages. Sure, it will release oils, etc, and that is necessary, but removing dirt requires mechanical action, and a steam machine, just because of the way steam works, just can't do it.
If that same contractor had nozzles that were less restrictive, he would likely be able to remove oils, etc, just as quick in a parking garage, and reduce the fuel consumption on his machines.
Of course, this is just my opinion. I may, or may not, be a legitimate contractor. I need to check with my accountant.