I use a 300gpd unit which produces around 700 litres a day and water comes out around 003-004 (200 in). My water pressure is 50-55psi. You should get better performnce as your water pressure is higher, unless membrane or pre-filters need changing.
4040 is around £450 plus I think which is why I like the small ro-man units as they work well and membranes are cheaper.