Ok - who on here uses different sized nozzles in the same machine or is it just me ? I must 5h1t at explaining this. If you run the revs flat out all of the time then ignor this but surely you must look at a wall thats painted and think I will remove all that paint so you knock back the revs and hence reduce the pressure ?
The OP if I read it correctly said he would use a smaller pump to increase the pressure - all I'm trying to get across is that his engine will still only rev to the same level so the smaller pump will only ever displace less water which will require a smaller nozzle.
Think as pressure as speed and flow as weight. If you rode a push bike into a wall at 40 mph and drove a lorry into the wall at 30 mph what would do the most damage ? This is why flow is more important than pressure. I have 250 bar @ 15 ltrs and a 200 bar @ 21 ltrs and the latter one cleans far better.