I know a guy around here (He is actually on PWI sometimes) who bought a 5.5 GPM 3500 PSI for residential cleaning, and ended up putting 2500 PSI nozzles in his surface cleaner anyway. 3500 PSI is too much for residential concrete. I am getting by just fine with 7 GPM and about 2000 PSI. Go with the 2500 PSI machine IF you are only doing residential. It will save you not only that initial investment, but probably a couple grand worth of gas per year.
I have posted this pic many places to prove this point, but I guess I'll keep posting it. Here is concrete cleaned with 7 GPM 2000 PSI, and pretreating with bleach and caustic downstreamed.
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