For years I had a 2000psi 1.7gpm unit that I took to the track religiously. A couple years ago when I tried it out at the house it developed a stuck valve over the winter. Unstuck said valve. Did not feel comfy taking it to the track, since now it was unreliable.
Bought a 3100psi 2.5gpm unit. I figured I might run out of water, since it upped my usage by .8 gpm. Wrong. I would say about the same. More pressure & flow equals less time to do the job.
But KMC440 is correct, I would not want a unit that is less than 1500psi, and that would be washing off dust. FYI at that pressure, if your dealing with REAL eastern sticky mud, you will go through that 55 gallon barrel in one wash.
YMMV