Strange isn't it, I have a small 200 gallon R/O, input TDS approx 0.150 ppm, output from R/O 0.002 ppm. and then 0.000 ppm after resin.
The current membranes (2 of them) are about a year old, prefilters around 6 months old and it takes about 30 hours to produce a 1000 litres at a tap pressure of 85 psi, and that is enough to keep two people supplied with pure water (me & squeaky).
So for me I see no reason to buy a 4040 R/O...but if my R/O was only bringing my output water down to something like 0.045 ppm I'd certainly be considering it.
What is the tap water TDS?
Correctly pressured, your R/O should be able to reduce the TDS by at least 95%
Ian