There are a lot of other variables to include in your decision making process like what size hose are you running to your surface cleaner from the hose reel, running hot water or cold or both, what size orifice nozzles, what spray pattern nozzles, how old the nozzles are, how dirty the concrete is, how strong the concrete is, etc......
I only use the big guy on large areas where it is not bad like dumpster pads, on the other stuff I use the 24" or 20" surface cleaners, they will get the job done faster overall when dealing with the very bad stuff and only 5.5gpm machine.