I'm doing well dave, are you of to the TACCA day?... might see you there
30lts a min will empty a wheely bin in 10mins you will need a high flow tap to keep up with your work or you will be constantly be stopping
if you are wanting reliability (as this is the last machine you will buy) then a bigger pump and engine will not equal more reliability
a small interpump is as reliable as a big interpump, does a 30hp engine last longer than a 20hp engine? if both are used at their optimum rate then both will give the same lifespan
an engine rated with a higher horsepower than the pump requires will allow the engine to be under less stress,, but you are buying a bigger pump so need a bigger engine.
it just looks like to me that you are spending money needlessly