Dave, like most things it varies on circumstances, the smaller RO systems process slowly so get to process the water to a lower TDS ( although there's not much in it 3 or 4 in the range )
RO 4040's esp with booster pump produce water at great speed mines nearly 200 ltrs p/h - speed and time saving is the biggest plus for me as we use between 1000 to 1500 ltrs per day, so something that takes 24 hrs to produce 1000 ltrs is unviable.
But due to the speed TDS is a little higher, I get a TDS of 10 from 320 way, way back I used a 420 GDP RO this gave 3 TDS
Not measured my waste ratio, it's set by pure freedom, but looks around 50/50
Darran