I subscribe to Tim's theory.......3000psi@4GPM as a minimum. That is what I started out with, and currently I am using 3000psi@5.5GPM. I could never go back to the 4gpm's. The 4 would be ideal for you to start though. Anything less could prove frustrating to you.
Like Tim said, figure the cleaning units
2300psi@2.5GPM = 5750 Cleaning Units
3000psi@4GPM = 12000 Cleaning Units
3000psi@5.5GPM = 16500 Cleaning Units
As you can see, the machine you are talking about has less then half of the capacity. Not that it would not be able to do the work you are describing, it would just take you twice as long. You dont have time for that, especially if you are just part time.
Best of luck in your hunt for the ideal equipment.
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Mike Hughes
Everclear
Souderton, PA